diff --git a/mobile/analysis_options.yaml b/mobile/analysis_options.yaml
index 21595e3e10..854f852e3c 100644
--- a/mobile/analysis_options.yaml
+++ b/mobile/analysis_options.yaml
@@ -35,6 +35,7 @@ linter:
 analyzer:
   exclude:
     - openapi/**
+    - build/**
     - lib/generated_plugin_registrant.dart
     - lib/**/*.g.dart
     - lib/**/*.drift.dart
@@ -147,7 +148,9 @@ dart_code_metrics:
     - avoid-global-state
     - avoid-inverted-boolean-checks
     - avoid-late-final-reassignment
-    - avoid-local-functions
+    - avoid-local-functions:
+        exclude:
+          - test/**.dart
     - avoid-negated-conditions
     - avoid-nested-streams-and-futures
     - avoid-referencing-subclasses
diff --git a/mobile/devtools_options.yaml b/mobile/devtools_options.yaml
index fa0b357c4f..f592d85a9b 100644
--- a/mobile/devtools_options.yaml
+++ b/mobile/devtools_options.yaml
@@ -1,3 +1,4 @@
 description: This file stores settings for Dart & Flutter DevTools.
 documentation: https://docs.flutter.dev/tools/devtools/extensions#configure-extension-enablement-states
 extensions:
+  - drift: true
\ No newline at end of file
diff --git a/mobile/lib/constants/constants.dart b/mobile/lib/constants/constants.dart
index b084effd91..a91e0a715d 100644
--- a/mobile/lib/constants/constants.dart
+++ b/mobile/lib/constants/constants.dart
@@ -5,6 +5,9 @@ const double downloadFailed = -2;
 // Number of log entries to retain on app start
 const int kLogTruncateLimit = 250;
 
+// Sync
+const int kSyncEventBatchSize = 5000;
+
 // Hash batch limits
 const int kBatchHashFileLimit = 128;
 const int kBatchHashSizeLimit = 1024 * 1024 * 1024; // 1GB
diff --git a/mobile/lib/domain/interfaces/sync_stream.interface.dart b/mobile/lib/domain/interfaces/sync_stream.interface.dart
index 0b2b5879f0..f9c52d7ee0 100644
--- a/mobile/lib/domain/interfaces/sync_stream.interface.dart
+++ b/mobile/lib/domain/interfaces/sync_stream.interface.dart
@@ -2,9 +2,9 @@ import 'package:immich_mobile/domain/interfaces/db.interface.dart';
 import 'package:openapi/api.dart';
 
 abstract interface class ISyncStreamRepository implements IDatabaseRepository {
-  Future<bool> updateUsersV1(SyncUserV1 data);
-  Future<bool> deleteUsersV1(SyncUserDeleteV1 data);
+  Future<bool> updateUsersV1(Iterable<SyncUserV1> data);
+  Future<bool> deleteUsersV1(Iterable<SyncUserDeleteV1> data);
 
-  Future<bool> updatePartnerV1(SyncPartnerV1 data);
-  Future<bool> deletePartnerV1(SyncPartnerDeleteV1 data);
+  Future<bool> updatePartnerV1(Iterable<SyncPartnerV1> data);
+  Future<bool> deletePartnerV1(Iterable<SyncPartnerDeleteV1> data);
 }
diff --git a/mobile/lib/domain/services/sync_stream.service.dart b/mobile/lib/domain/services/sync_stream.service.dart
index e710fba1b4..57c8ec72fd 100644
--- a/mobile/lib/domain/services/sync_stream.service.dart
+++ b/mobile/lib/domain/services/sync_stream.service.dart
@@ -2,6 +2,7 @@
 
 import 'dart:async';
 
+import 'package:collection/collection.dart';
 import 'package:immich_mobile/domain/interfaces/sync_api.interface.dart';
 import 'package:immich_mobile/domain/interfaces/sync_stream.interface.dart';
 import 'package:logging/logging.dart';
@@ -19,79 +20,122 @@ class SyncStreamService {
   })  : _syncApiRepository = syncApiRepository,
         _syncStreamRepository = syncStreamRepository;
 
-  // ignore: avoid-dynamic
-  Future<bool> _handleSyncData(dynamic data) async {
-    if (data is SyncPartnerV1) {
-      _logger.fine("SyncPartnerV1: $data");
-      return await _syncStreamRepository.updatePartnerV1(data);
+  Future<bool> _handleSyncData(
+    SyncEntityType type,
+    // ignore: avoid-dynamic
+    Iterable<dynamic> data,
+  ) async {
+    if (data.isEmpty) {
+      _logger.warning("Received empty sync data for $type");
+      return false;
     }
 
-    if (data is SyncUserV1) {
-      _logger.fine("SyncUserV1: $data");
-      return await _syncStreamRepository.updateUsersV1(data);
-    }
-
-    if (data is SyncPartnerDeleteV1) {
-      _logger.fine("SyncPartnerDeleteV1: $data");
-      return await _syncStreamRepository.deletePartnerV1(data);
-    }
-
-    if (data is SyncUserDeleteV1) {
-      _logger.fine("SyncUserDeleteV1: $data");
-      return await _syncStreamRepository.deleteUsersV1(data);
+    _logger.fine("Processing sync data for $type of length ${data.length}");
+
+    try {
+      if (type == SyncEntityType.partnerV1) {
+        return await _syncStreamRepository.updatePartnerV1(data.cast());
+      }
+
+      if (type == SyncEntityType.partnerDeleteV1) {
+        return await _syncStreamRepository.deletePartnerV1(data.cast());
+      }
+
+      if (type == SyncEntityType.userV1) {
+        return await _syncStreamRepository.updateUsersV1(data.cast());
+      }
+
+      if (type == SyncEntityType.userDeleteV1) {
+        return await _syncStreamRepository.deleteUsersV1(data.cast());
+      }
+    } catch (error, stack) {
+      _logger.severe("Error processing sync data for $type", error, stack);
+      return false;
     }
 
+    _logger.warning("Unknown sync data type: $type");
     return false;
   }
 
   Future<void> _syncEvent(List<SyncRequestType> types) async {
     _logger.info("Syncing Events: $types");
     final streamCompleter = Completer();
-    bool shouldSkipOnDone = false;
+    bool shouldComplete = false;
+    // the onDone callback might fire before the events are processed
+    // the following flag ensures that the onDone callback is not called
+    // before the events are processed and also that events are processed sequentially
+    Completer? mutex;
     final subscription = _syncApiRepository.getSyncEvents(types).listen(
       (events) async {
+        if (events.isEmpty) {
+          _logger.warning("Received empty sync events");
+          return;
+        }
+
+        // If previous events are still being processed, wait for them to finish
+        if (mutex != null) {
+          await mutex!.future;
+        }
+
+        // Take control of the mutex and process the events
+        mutex = Completer();
+
         try {
-          Map<SyncEntityType, String> acks = {};
-          for (final event in events) {
-            // the onDone callback might fire before the events are processed
-            // the following flag ensures that the onDone callback is not called
-            // before the events are processed
-            shouldSkipOnDone = true;
-            if (await _handleSyncData(event.data)) {
-              // Only retain the latest ack from each type
-              acks[event.type] = event.ack;
+          final eventsMap = events.groupListsBy((event) => event.type);
+          final Map<SyncEntityType, String> acks = {};
+
+          for (final entry in eventsMap.entries) {
+            final type = entry.key;
+            final data = entry.value;
+
+            if (data.isEmpty) {
+              _logger.warning("Received empty sync events for $type");
+              continue;
+            }
+
+            if (await _handleSyncData(type, data.map((e) => e.data))) {
+              // ignore: avoid-unsafe-collection-methods
+              acks[type] = data.last.ack;
+            } else {
+              _logger.warning("Failed to handle sync events for $type");
             }
           }
-          await _syncApiRepository.ack(acks.values.toList());
+
+          if (acks.isNotEmpty) {
+            await _syncApiRepository.ack(acks.values.toList());
+          }
           _logger.info("$types events processed");
         } catch (error, stack) {
           _logger.warning("Error handling sync events", error, stack);
+        } finally {
+          mutex?.complete();
+          mutex = null;
+        }
+
+        if (shouldComplete) {
+          _logger.info("Sync done, completing stream");
+          if (!streamCompleter.isCompleted) streamCompleter.complete();
         }
-        streamCompleter.completeOnce();
       },
-      onError: (error) {
-        _logger.warning("Error in sync stream for $types", error);
-        streamCompleter.completeOnce();
+      onError: (error, stack) {
+        _logger.warning("Error in sync stream for $types", error, stack);
+        // Do not proceed if the stream errors
+        if (!streamCompleter.isCompleted) streamCompleter.complete();
       },
-      // onDone is required to be called in cases where the stream is empty
       onDone: () {
         _logger.info("$types stream done");
-        if (!shouldSkipOnDone) {
-          streamCompleter.completeOnce();
+        if (mutex == null && !streamCompleter.isCompleted) {
+          streamCompleter.complete();
+        } else {
+          // Marks the stream as done but does not complete the completer
+          // until the events are processed
+          shouldComplete = true;
         }
       },
     );
     return await streamCompleter.future.whenComplete(subscription.cancel);
   }
 
-  Future<void> syncUsers() => _syncEvent([SyncRequestType.usersV1]);
-  Future<void> syncPartners() => _syncEvent([SyncRequestType.partnersV1]);
-}
-
-extension on Completer {
-  void completeOnce() {
-    if (!isCompleted) {
-      complete();
-    }
-  }
+  Future<void> syncUsers() =>
+      _syncEvent([SyncRequestType.usersV1, SyncRequestType.partnersV1]);
 }
diff --git a/mobile/lib/extensions/string_extensions.dart b/mobile/lib/extensions/string_extensions.dart
index 293618df0b..73c8c2d34c 100644
--- a/mobile/lib/extensions/string_extensions.dart
+++ b/mobile/lib/extensions/string_extensions.dart
@@ -35,5 +35,6 @@ extension DurationExtension on String {
 }
 
 extension UUIDExtension on String {
-  Uint8List toUuidByte() => UuidParsing.parseAsByteList(this);
+  Uint8List toUuidByte({bool shouldValidate = false}) =>
+      UuidParsing.parseAsByteList(this, validate: shouldValidate);
 }
diff --git a/mobile/lib/infrastructure/repositories/sync_api.repository.dart b/mobile/lib/infrastructure/repositories/sync_api.repository.dart
index 916d5f4740..a26b867df6 100644
--- a/mobile/lib/infrastructure/repositories/sync_api.repository.dart
+++ b/mobile/lib/infrastructure/repositories/sync_api.repository.dart
@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:convert';
 
 import 'package:http/http.dart' as http;
+import 'package:immich_mobile/constants/constants.dart';
 import 'package:immich_mobile/domain/interfaces/sync_api.interface.dart';
 import 'package:immich_mobile/domain/models/sync_event.model.dart';
 import 'package:immich_mobile/services/api.service.dart';
@@ -11,7 +12,9 @@ import 'package:openapi/api.dart';
 class SyncApiRepository implements ISyncApiRepository {
   final Logger _logger = Logger('SyncApiRepository');
   final ApiService _api;
-  SyncApiRepository(this._api);
+  final int _batchSize;
+  SyncApiRepository(this._api, {int batchSize = kSyncEventBatchSize})
+      : _batchSize = batchSize;
 
   @override
   Stream<List<SyncEvent>> getSyncEvents(List<SyncRequestType> type) {
@@ -23,10 +26,7 @@ class SyncApiRepository implements ISyncApiRepository {
     return _api.syncApi.sendSyncAck(SyncAckSetDto(acks: data));
   }
 
-  Stream<List<SyncEvent>> _getSyncStream(
-    SyncStreamDto dto, {
-    int batchSize = 5000,
-  }) async* {
+  Stream<List<SyncEvent>> _getSyncStream(SyncStreamDto dto) async* {
     final client = http.Client();
     final endpoint = "${_api.apiClient.basePath}/sync/stream";
 
@@ -64,7 +64,7 @@ class SyncApiRepository implements ISyncApiRepository {
         previousChunk = parts.removeLast();
         lines.addAll(parts);
 
-        if (lines.length < batchSize) {
+        if (lines.length < _batchSize) {
           continue;
         }
 
@@ -90,7 +90,7 @@ class SyncApiRepository implements ISyncApiRepository {
         final ack = jsonData['ack'];
         final converter = _kResponseMap[type];
         if (converter == null) {
-          _logger.warning("[_parseSyncReponse] Unknown type $type");
+          _logger.warning("[_parseSyncResponse] Unknown type $type");
           continue;
         }
 
diff --git a/mobile/lib/infrastructure/repositories/sync_stream.repository.dart b/mobile/lib/infrastructure/repositories/sync_stream.repository.dart
index f85b50c220..a947a9a66b 100644
--- a/mobile/lib/infrastructure/repositories/sync_stream.repository.dart
+++ b/mobile/lib/infrastructure/repositories/sync_stream.repository.dart
@@ -15,11 +15,16 @@ class DriftSyncStreamRepository extends DriftDatabaseRepository
   DriftSyncStreamRepository(super.db) : _db = db;
 
   @override
-  Future<bool> deleteUsersV1(SyncUserDeleteV1 data) async {
+  Future<bool> deleteUsersV1(Iterable<SyncUserDeleteV1> data) async {
     try {
-      await _db.managers.userEntity
-          .filter((row) => row.id.equals(data.userId.toUuidByte()))
-          .delete();
+      await _db.batch((batch) {
+        for (final user in data) {
+          batch.delete(
+            _db.userEntity,
+            UserEntityCompanion(id: Value(user.userId.toUuidByte())),
+          );
+        }
+      });
       return true;
     } catch (e, s) {
       _logger.severe('Error while processing SyncUserDeleteV1', e, s);
@@ -28,17 +33,22 @@ class DriftSyncStreamRepository extends DriftDatabaseRepository
   }
 
   @override
-  Future<bool> updateUsersV1(SyncUserV1 data) async {
-    final companion = UserEntityCompanion(
-      name: Value(data.name),
-      email: Value(data.email),
-    );
-
+  Future<bool> updateUsersV1(Iterable<SyncUserV1> data) async {
     try {
-      await _db.userEntity.insertOne(
-        companion.copyWith(id: Value(data.id.toUuidByte())),
-        onConflict: DoUpdate((_) => companion),
-      );
+      await _db.batch((batch) {
+        for (final user in data) {
+          final companion = UserEntityCompanion(
+            name: Value(user.name),
+            email: Value(user.email),
+          );
+
+          batch.insert(
+            _db.userEntity,
+            companion.copyWith(id: Value(user.id.toUuidByte())),
+            onConflict: DoUpdate((_) => companion),
+          );
+        }
+      });
       return true;
     } catch (e, s) {
       _logger.severe('Error while processing SyncUserV1', e, s);
@@ -47,15 +57,19 @@ class DriftSyncStreamRepository extends DriftDatabaseRepository
   }
 
   @override
-  Future<bool> deletePartnerV1(SyncPartnerDeleteV1 data) async {
+  Future<bool> deletePartnerV1(Iterable<SyncPartnerDeleteV1> data) async {
     try {
-      await _db.managers.partnerEntity
-          .filter(
-            (row) =>
-                row.sharedById.id.equals(data.sharedById.toUuidByte()) &
-                row.sharedWithId.id.equals(data.sharedWithId.toUuidByte()),
-          )
-          .delete();
+      await _db.batch((batch) {
+        for (final partner in data) {
+          batch.delete(
+            _db.partnerEntity,
+            PartnerEntityCompanion(
+              sharedById: Value(partner.sharedById.toUuidByte()),
+              sharedWithId: Value(partner.sharedWithId.toUuidByte()),
+            ),
+          );
+        }
+      });
       return true;
     } catch (e, s) {
       _logger.severe('Error while processing SyncPartnerDeleteV1', e, s);
@@ -64,18 +78,23 @@ class DriftSyncStreamRepository extends DriftDatabaseRepository
   }
 
   @override
-  Future<bool> updatePartnerV1(SyncPartnerV1 data) async {
-    final companion =
-        PartnerEntityCompanion(inTimeline: Value(data.inTimeline));
-
+  Future<bool> updatePartnerV1(Iterable<SyncPartnerV1> data) async {
     try {
-      await _db.partnerEntity.insertOne(
-        companion.copyWith(
-          sharedById: Value(data.sharedById.toUuidByte()),
-          sharedWithId: Value(data.sharedWithId.toUuidByte()),
-        ),
-        onConflict: DoUpdate((_) => companion),
-      );
+      await _db.batch((batch) {
+        for (final partner in data) {
+          final companion =
+              PartnerEntityCompanion(inTimeline: Value(partner.inTimeline));
+
+          batch.insert(
+            _db.partnerEntity,
+            companion.copyWith(
+              sharedById: Value(partner.sharedById.toUuidByte()),
+              sharedWithId: Value(partner.sharedWithId.toUuidByte()),
+            ),
+            onConflict: DoUpdate((_) => companion),
+          );
+        }
+      });
       return true;
     } catch (e, s) {
       _logger.severe('Error while processing SyncPartnerV1', e, s);
diff --git a/mobile/lib/utils/background_sync.dart b/mobile/lib/utils/background_sync.dart
index bfedbf2601..906a548cbe 100644
--- a/mobile/lib/utils/background_sync.dart
+++ b/mobile/lib/utils/background_sync.dart
@@ -9,7 +9,6 @@ import 'package:immich_mobile/utils/isolate.dart';
 class BackgroundSyncManager {
   // This prevents multiple syncs from running at the same time
   final _userSyncCache = AsyncCache.ephemeral();
-  final _partnerSyncCache = AsyncCache.ephemeral();
 
   BackgroundSyncManager();
 
@@ -18,10 +17,4 @@ class BackgroundSyncManager {
           (ref) => ref.read(syncStreamServiceProvider).syncUsers(),
         ),
       );
-
-  Future<void> syncPartners() => _partnerSyncCache.fetch(
-        () async => runInIsolate(
-          (ref) => ref.read(syncStreamServiceProvider).syncPartners(),
-        ),
-      );
 }
diff --git a/mobile/test/domain/services/sync_stream_service_test.dart b/mobile/test/domain/services/sync_stream_service_test.dart
index e5cfbd0ccc..aa4ab9d896 100644
--- a/mobile/test/domain/services/sync_stream_service_test.dart
+++ b/mobile/test/domain/services/sync_stream_service_test.dart
@@ -1,8 +1,11 @@
+// ignore_for_file: avoid-unnecessary-futures
+
 import 'dart:async';
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:immich_mobile/domain/interfaces/sync_api.interface.dart';
 import 'package:immich_mobile/domain/interfaces/sync_stream.interface.dart';
+import 'package:immich_mobile/domain/models/sync_event.model.dart';
 import 'package:immich_mobile/domain/services/sync_stream.service.dart';
 import 'package:mocktail/mocktail.dart';
 import 'package:openapi/api.dart';
@@ -14,105 +17,314 @@ void main() {
   late SyncStreamService sut;
   late ISyncStreamRepository mockSyncStreamRepo;
   late ISyncApiRepository mockSyncApiRepo;
+  late StreamController<List<SyncEvent>> streamController;
+
+  successHandler(Invocation _) async => true;
+  failureHandler(Invocation _) async => false;
 
   setUp(() {
     mockSyncStreamRepo = MockSyncStreamRepository();
     mockSyncApiRepo = MockSyncApiRepository();
+    streamController = StreamController<List<SyncEvent>>.broadcast();
+
     sut = SyncStreamService(
       syncApiRepository: mockSyncApiRepo,
       syncStreamRepository: mockSyncStreamRepo,
     );
 
-    when(() => mockSyncApiRepo.getSyncEvents([SyncRequestType.usersV1]))
-        .thenAnswer((_) => Stream.value(SyncStreamStub.userEvents));
-    when(() => mockSyncApiRepo.getSyncEvents([SyncRequestType.partnersV1]))
-        .thenAnswer((_) => Stream.value(SyncStreamStub.partnerEvents));
-    when(() => mockSyncApiRepo.ack(any())).thenAnswer((_) => Future.value());
+    // Default stream setup - emits one batch and closes
+    when(() => mockSyncApiRepo.getSyncEvents(any()))
+        .thenAnswer((_) => streamController.stream);
 
-    registerFallbackValue(SyncStreamStub.userV1Admin);
+    // Default ack setup
+    when(() => mockSyncApiRepo.ack(any())).thenAnswer((_) async => {});
+
+    // Register fallbacks for mocktail verification
+    registerFallbackValue(<SyncUserV1>[]);
+    registerFallbackValue(<SyncPartnerV1>[]);
+    registerFallbackValue(<SyncUserDeleteV1>[]);
+    registerFallbackValue(<SyncPartnerDeleteV1>[]);
+
+    // Default successful repository calls
     when(() => mockSyncStreamRepo.updateUsersV1(any()))
-        .thenAnswer((_) => Future.value(true));
-    registerFallbackValue(SyncStreamStub.partnerV1);
-    when(() => mockSyncStreamRepo.updatePartnerV1(any()))
-        .thenAnswer((_) => Future.value(false));
-    registerFallbackValue(SyncStreamStub.userDeleteV1);
+        .thenAnswer(successHandler);
     when(() => mockSyncStreamRepo.deleteUsersV1(any()))
-        .thenAnswer((_) => Future.value(false));
-    registerFallbackValue(SyncStreamStub.partnerDeleteV1);
+        .thenAnswer(successHandler);
+    when(() => mockSyncStreamRepo.updatePartnerV1(any()))
+        .thenAnswer(successHandler);
     when(() => mockSyncStreamRepo.deletePartnerV1(any()))
-        .thenAnswer((_) => Future.value(true));
+        .thenAnswer(successHandler);
   });
 
-  group("_syncEvent", () {
-    test("future completed on success", () async {
+  tearDown(() async {
+    await streamController.close();
+  });
+
+  // Helper to trigger sync and add events to the stream
+  Future<void> triggerSyncAndEmit(List<SyncEvent> events) async {
+    final future = sut.syncUsers(); // Start listening
+    await Future.delayed(Duration.zero); // Allow listener to attach
+    if (!streamController.isClosed) {
+      streamController.add(events);
+      await streamController.close(); // Close after emitting
+    }
+    await future; // Wait for processing to complete
+  }
+
+  group("SyncStreamService", () {
+    test(
+      "completes successfully when stream emits data and handlers succeed",
+      () async {
+        final events = [
+          ...SyncStreamStub.userEvents,
+          ...SyncStreamStub.partnerEvents,
+        ];
+        final future = triggerSyncAndEmit(events);
+        await expectLater(future, completes);
+        // Verify ack includes last ack from each successfully handled type
+        verify(
+          () => mockSyncApiRepo
+              .ack(any(that: containsAllInOrder(["5", "2", "4", "3"]))),
+        ).called(1);
+      },
+    );
+
+    test("completes successfully when stream emits an error", () async {
+      when(() => mockSyncApiRepo.getSyncEvents(any()))
+          .thenAnswer((_) => Stream.error(Exception("Stream Error")));
+      // Should complete gracefully without throwing
       await expectLater(sut.syncUsers(), completes);
+      verifyNever(() => mockSyncApiRepo.ack(any())); // No ack on stream error
     });
 
-    test("future completes on error from stream", () async {
-      when(() => mockSyncApiRepo.getSyncEvents([SyncRequestType.usersV1]))
-          .thenAnswer((_) => Stream.error(Exception("Error")));
-      await expectLater(sut.syncUsers(), completes);
+    test("throws when initial getSyncEvents call fails", () async {
+      final apiException = Exception("API Error");
+      when(() => mockSyncApiRepo.getSyncEvents(any())).thenThrow(apiException);
+      // Should rethrow the exception from the initial call
+      await expectLater(sut.syncUsers(), throwsA(apiException));
+      verifyNever(() => mockSyncApiRepo.ack(any()));
     });
 
-    test("future throws on api exception", () {
-      when(() => mockSyncApiRepo.getSyncEvents([SyncRequestType.usersV1]))
-          .thenThrow(Exception("Error"));
-      expect(sut.syncUsers(), throwsA(isA<Exception>()));
-    });
+    test(
+      "completes successfully when a repository handler throws an exception",
+      () async {
+        when(() => mockSyncStreamRepo.updateUsersV1(any()))
+            .thenThrow(Exception("Repo Error"));
+        final events = [
+          ...SyncStreamStub.userEvents,
+          ...SyncStreamStub.partnerEvents,
+        ];
+        // Should complete, but ack only for the successful types
+        await triggerSyncAndEmit(events);
+        // Only partner delete was successful by default setup
+        verify(() => mockSyncApiRepo.ack(["2", "4", "3"])).called(1);
+      },
+    );
 
-    test("future completes on repository exception", () {
+    test(
+      "completes successfully but sends no ack when all handlers fail",
+      () async {
+        when(() => mockSyncStreamRepo.updateUsersV1(any()))
+            .thenAnswer(failureHandler);
+        when(() => mockSyncStreamRepo.deleteUsersV1(any()))
+            .thenAnswer(failureHandler);
+        when(() => mockSyncStreamRepo.updatePartnerV1(any()))
+            .thenAnswer(failureHandler);
+        when(() => mockSyncStreamRepo.deletePartnerV1(any()))
+            .thenAnswer(failureHandler);
+
+        final events = [
+          ...SyncStreamStub.userEvents,
+          ...SyncStreamStub.partnerEvents,
+        ];
+        await triggerSyncAndEmit(events);
+        verifyNever(() => mockSyncApiRepo.ack(any()));
+      },
+    );
+
+    test("sends ack only for types where handler returns true", () async {
+      // Mock specific handlers: user update fails, user delete succeeds
       when(() => mockSyncStreamRepo.updateUsersV1(any()))
-          .thenThrow(Exception("Error"));
-      expect(sut.syncUsers(), completes);
-    });
-
-    test("sends ack for successful events", () async {
-      when(() => mockSyncStreamRepo.updateUsersV1(any()))
-          .thenAnswer((_) => Future.value(false));
+          .thenAnswer(failureHandler);
       when(() => mockSyncStreamRepo.deleteUsersV1(any()))
-          .thenAnswer((_) => Future.value(true));
-      await sut.syncUsers();
-      verify(() => mockSyncApiRepo.ack(["2"])).called(1);
+          .thenAnswer(successHandler);
+      // partner update fails, partner delete succeeds
+      when(() => mockSyncStreamRepo.updatePartnerV1(any()))
+          .thenAnswer(failureHandler);
+
+      final events = [
+        ...SyncStreamStub.userEvents,
+        ...SyncStreamStub.partnerEvents,
+      ];
+      await triggerSyncAndEmit(events);
+
+      // Expect ack only for userDeleteV1 (ack: "2") and partnerDeleteV1 (ack: "4")
+      verify(
+        () => mockSyncApiRepo.ack(any(that: containsAllInOrder(["2", "4"]))),
+      ).called(1);
     });
 
-    test("only sends the latest ack for events of same type", () async {
-      await sut.syncUsers();
-      verify(() => mockSyncApiRepo.ack(["5"])).called(1);
+    test("does not process or ack when stream emits an empty list", () async {
+      final future = sut.syncUsers();
+      streamController.add([]); // Emit empty list
+      await streamController.close();
+      await future; // Wait for completion
+
+      verifyNever(() => mockSyncStreamRepo.updateUsersV1(any()));
+      verifyNever(() => mockSyncStreamRepo.deleteUsersV1(any()));
+      verifyNever(() => mockSyncStreamRepo.updatePartnerV1(any()));
+      verifyNever(() => mockSyncStreamRepo.deletePartnerV1(any()));
+      verifyNever(() => mockSyncApiRepo.ack(any()));
+    });
+
+    test("processes multiple batches sequentially using mutex", () async {
+      final completer1 = Completer<void>();
+      final completer2 = Completer<void>();
+      int callOrder = 0;
+      int handler1StartOrder = -1;
+      int handler2StartOrder = -1;
+
+      when(() => mockSyncStreamRepo.updateUsersV1(any())).thenAnswer((_) async {
+        handler1StartOrder = ++callOrder; // Record when handler 1 starts
+        await completer1.future; // Wait for external signal
+        return true;
+      });
+      when(() => mockSyncStreamRepo.updatePartnerV1(any()))
+          .thenAnswer((_) async {
+        handler2StartOrder = ++callOrder; // Record when handler 2 starts
+        await completer2.future;
+        return true;
+      });
+
+      final batch1 = SyncStreamStub.userEvents;
+      final batch2 = SyncStreamStub.partnerEvents;
+
+      final syncFuture = sut.syncUsers();
+      streamController.add(batch1); // Emit first batch
+
+      // Ensure first batch processing starts
+      await Future.delayed(const Duration(milliseconds: 10));
+      expect(handler1StartOrder, 1, reason: "Handler 1 should start first");
+
+      streamController.add(batch2); // Emit second batch while first is waiting
+
+      await Future.delayed(const Duration(milliseconds: 10));
+      // Handler 2 should NOT have started yet because mutex is held by handler 1
+      expect(
+        handler2StartOrder,
+        -1,
+        reason: "Handler 2 should wait for Handler 1",
+      );
+
+      completer1.complete(); // Allow first handler to finish
+      // Allow second batch to start processing
+      await Future.delayed(const Duration(milliseconds: 10));
+
+      // Now handler 2 should start
+      expect(
+        handler2StartOrder,
+        2,
+        reason: "Handler 2 should start after Handler 1 finishes",
+      );
+
+      completer2.complete(); // Allow second handler to finish
+      await streamController.close(); // Close stream
+      await syncFuture; // Wait for overall completion
+
+      // Verify handlers were called and acks sent for both batches eventually
+      verify(() => mockSyncStreamRepo.updateUsersV1(any())).called(1);
+      verify(() => mockSyncStreamRepo.updatePartnerV1(any())).called(1);
+      // Acks might be called separately or combined depending on timing, check count
+      verify(() => mockSyncApiRepo.ack(any())).called(2);
+    });
+
+    test("completes successfully when ack call throws an exception", () async {
+      when(() => mockSyncApiRepo.ack(any())).thenThrow(Exception("Ack Error"));
+      final events = [
+        ...SyncStreamStub.userEvents,
+        ...SyncStreamStub.partnerEvents,
+      ];
+
+      // Should still complete even if ack fails
+      await triggerSyncAndEmit(events);
+      verify(() => mockSyncApiRepo.ack(any()))
+          .called(1); // Verify ack was attempted
+    });
+
+    test("waits for processing to finish if onDone called early", () async {
+      final processingCompleter = Completer<void>();
+      bool handlerFinished = false;
+
+      when(() => mockSyncStreamRepo.updateUsersV1(any())).thenAnswer((_) async {
+        await processingCompleter.future; // Wait inside handler
+        handlerFinished = true;
+        return true;
+      });
+
+      final syncFuture = sut.syncUsers();
+      // Allow listener to attach
+      // This is necessary to ensure the stream is ready to receive events
+      await Future.delayed(Duration.zero);
+
+      streamController.add(SyncStreamStub.userEvents); // Emit batch
+      await Future.delayed(
+        const Duration(milliseconds: 10),
+      ); // Ensure processing starts
+
+      await streamController
+          .close(); // Close stream (triggers onDone internally)
+      await Future.delayed(
+        const Duration(milliseconds: 10),
+      ); // Give onDone a chance to fire
+
+      // At this point, onDone was called, but processing is blocked
+      expect(handlerFinished, isFalse);
+
+      processingCompleter.complete(); // Allow processing to finish
+      await syncFuture; // Now the main future should complete
+
+      expect(handlerFinished, isTrue);
+      verify(() => mockSyncApiRepo.ack(any())).called(1);
     });
   });
 
   group("syncUsers", () {
-    test("calls _syncEvent with usersV1", () async {
-      await sut.syncUsers();
-      verify(() => mockSyncApiRepo.getSyncEvents([SyncRequestType.usersV1]))
-          .called(1);
-    });
+    test("calls getSyncEvents with correct types", () async {
+      // Need to close the stream for the future to complete
+      final future = sut.syncUsers();
+      await streamController.close();
+      await future;
 
-    test("calls _handleSyncData for each event", () async {
-      await sut.syncUsers();
-      verify(() => mockSyncStreamRepo.updateUsersV1(SyncStreamStub.userV1Admin))
-          .called(1);
       verify(
-        () => mockSyncStreamRepo.deleteUsersV1(SyncStreamStub.userDeleteV1),
+        () => mockSyncApiRepo.getSyncEvents([
+          SyncRequestType.usersV1,
+          SyncRequestType.partnersV1,
+        ]),
       ).called(1);
     });
-  });
 
-  group("syncPartners", () {
-    test("calls _syncEvent with partnersV1", () async {
-      await sut.syncPartners();
-      verify(() => mockSyncApiRepo.getSyncEvents([SyncRequestType.partnersV1]))
-          .called(1);
-    });
+    test("calls repository methods with correctly grouped data", () async {
+      final events = [
+        ...SyncStreamStub.userEvents,
+        ...SyncStreamStub.partnerEvents,
+      ];
+      await triggerSyncAndEmit(events);
 
-    test("calls _handleSyncData for each event", () async {
-      await sut.syncPartners();
+      // Verify each handler was called with the correct list of data payloads
       verify(
-        () => mockSyncStreamRepo.updatePartnerV1(SyncStreamStub.partnerV1),
+        () => mockSyncStreamRepo.updateUsersV1(
+          [SyncStreamStub.userV1Admin, SyncStreamStub.userV1User],
+        ),
       ).called(1);
       verify(
-        () =>
-            mockSyncStreamRepo.deletePartnerV1(SyncStreamStub.partnerDeleteV1),
+        () => mockSyncStreamRepo.deleteUsersV1([SyncStreamStub.userDeleteV1]),
+      ).called(1);
+      verify(
+        () => mockSyncStreamRepo.updatePartnerV1([SyncStreamStub.partnerV1]),
+      ).called(1);
+      verify(
+        () => mockSyncStreamRepo
+            .deletePartnerV1([SyncStreamStub.partnerDeleteV1]),
       ).called(1);
     });
   });
diff --git a/mobile/test/fixtures/sync_stream.stub.dart b/mobile/test/fixtures/sync_stream.stub.dart
index d52de43662..781e63a2bb 100644
--- a/mobile/test/fixtures/sync_stream.stub.dart
+++ b/mobile/test/fixtures/sync_stream.stub.dart
@@ -35,11 +35,11 @@ abstract final class SyncStreamStub {
     sharedWithId: "4",
   );
   static final partnerEvents = [
-    SyncEvent(type: SyncEntityType.partnerV1, data: partnerV1, ack: "3"),
     SyncEvent(
       type: SyncEntityType.partnerDeleteV1,
       data: partnerDeleteV1,
       ack: "4",
     ),
+    SyncEvent(type: SyncEntityType.partnerV1, data: partnerV1, ack: "3"),
   ];
 }
diff --git a/mobile/test/service.mocks.dart b/mobile/test/service.mocks.dart
index e1b8df40a3..87a8c01cf0 100644
--- a/mobile/test/service.mocks.dart
+++ b/mobile/test/service.mocks.dart
@@ -29,4 +29,3 @@ class MockSearchApi extends Mock implements SearchApi {}
 class MockAppSettingService extends Mock implements AppSettingsService {}
 
 class MockBackgroundService extends Mock implements BackgroundService {}
-