diff --git a/.github/workflows/app.yml b/.github/workflows/app.yml
index 5593a080..91e5529d 100644
--- a/.github/workflows/app.yml
+++ b/.github/workflows/app.yml
@@ -50,14 +50,15 @@ jobs:
           retention-days: 1
 
   coverage:
-    runs-on: arm-ubuntu-latest-16core
+    #runs-on: arm-ubuntu-latest-16core
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - run: cat .github/workflows/versions.env >> $GITHUB_ENV
       - uses: dart-lang/setup-dart@a57a6c04cf7d4840e88432aad6281d1e125f0d46
         with:
           sdk: ${{ env.dart_version }}
-          architecture: "arm64"
+          #architecture: "arm64"
       - name: Run tests
         run: |
           sudo apt-get update && sudo apt-get install --no-install-recommends --no-install-suggests -y lcov libsqlite3-0 libsqlite3-dev libolm3 libssl3
diff --git a/.github/workflows/versions.env b/.github/workflows/versions.env
index a78fec4b..a1149f57 100644
--- a/.github/workflows/versions.env
+++ b/.github/workflows/versions.env
@@ -1,2 +1,2 @@
 flutter_version=3.22.2
-dart_version=3.4.3
+dart_version=3.5.3
diff --git a/lib/encryption/olm_manager.dart b/lib/encryption/olm_manager.dart
index d44116d3..37bce332 100644
--- a/lib/encryption/olm_manager.dart
+++ b/lib/encryption/olm_manager.dart
@@ -28,6 +28,7 @@ import 'package:matrix/encryption/utils/json_signature_check_extension.dart';
 import 'package:matrix/encryption/utils/olm_session.dart';
 import 'package:matrix/matrix.dart';
 import 'package:matrix/msc_extensions/msc_3814_dehydrated_devices/api.dart';
+import 'package:matrix/src/utils/run_benchmarked.dart';
 import 'package:matrix/src/utils/run_in_root.dart';
 
 class OlmManager {
@@ -326,43 +327,50 @@ class OlmManager {
     return false;
   }
 
+  final _otkUpdateDedup = AsyncCache<void>.ephemeral();
+
   Future<void> handleDeviceOneTimeKeysCount(
       Map<String, int>? countJson, List<String>? unusedFallbackKeyTypes) async {
     if (!enabled) {
       return;
     }
-    final haveFallbackKeys = encryption.isMinOlmVersion(3, 2, 0);
-    // Check if there are at least half of max_number_of_one_time_keys left on the server
-    // and generate and upload more if not.
 
-    // If the server did not send us a count, assume it is 0
-    final keyCount = countJson?.tryGet<int>('signed_curve25519') ?? 0;
+    await _otkUpdateDedup.fetch(() =>
+        runBenchmarked('handleOtkUpdate', () async {
+          final haveFallbackKeys = encryption.isMinOlmVersion(3, 2, 0);
+          // Check if there are at least half of max_number_of_one_time_keys left on the server
+          // and generate and upload more if not.
 
-    // If the server does not support fallback keys, it will not tell us about them.
-    // If the server supports them but has no key, upload a new one.
-    var unusedFallbackKey = true;
-    if (unusedFallbackKeyTypes?.contains('signed_curve25519') == false) {
-      unusedFallbackKey = false;
-    }
+          // If the server did not send us a count, assume it is 0
+          final keyCount = countJson?.tryGet<int>('signed_curve25519') ?? 0;
 
-    // fixup accidental too many uploads. We delete only one of them so that the server has time to update the counts and because we will get rate limited anyway.
-    if (keyCount > _olmAccount!.max_number_of_one_time_keys()) {
-      final requestingKeysFrom = {
-        client.userID!: {ourDeviceId!: 'signed_curve25519'}
-      };
-      await client.claimKeys(requestingKeysFrom, timeout: 10000);
-    }
+          // If the server does not support fallback keys, it will not tell us about them.
+          // If the server supports them but has no key, upload a new one.
+          var unusedFallbackKey = true;
+          if (unusedFallbackKeyTypes?.contains('signed_curve25519') == false) {
+            unusedFallbackKey = false;
+          }
 
-    // Only upload keys if they are less than half of the max or we have no unused fallback key
-    if (keyCount < (_olmAccount!.max_number_of_one_time_keys() / 2) ||
-        !unusedFallbackKey) {
-      await uploadKeys(
-        oldKeyCount: keyCount < (_olmAccount!.max_number_of_one_time_keys() / 2)
-            ? keyCount
-            : null,
-        unusedFallbackKey: haveFallbackKeys ? unusedFallbackKey : null,
-      );
-    }
+          // fixup accidental too many uploads. We delete only one of them so that the server has time to update the counts and because we will get rate limited anyway.
+          if (keyCount > _olmAccount!.max_number_of_one_time_keys()) {
+            final requestingKeysFrom = {
+              client.userID!: {ourDeviceId!: 'signed_curve25519'}
+            };
+            await client.claimKeys(requestingKeysFrom, timeout: 10000);
+          }
+
+          // Only upload keys if they are less than half of the max or we have no unused fallback key
+          if (keyCount < (_olmAccount!.max_number_of_one_time_keys() / 2) ||
+              !unusedFallbackKey) {
+            await uploadKeys(
+              oldKeyCount:
+                  keyCount < (_olmAccount!.max_number_of_one_time_keys() / 2)
+                      ? keyCount
+                      : null,
+              unusedFallbackKey: haveFallbackKeys ? unusedFallbackKey : null,
+            );
+          }
+        }));
   }
 
   Future<void> storeOlmSession(OlmSession session) async {
diff --git a/lib/fake_matrix_api.dart b/lib/fake_matrix_api.dart
index c78d1aae..8d96a4b3 100644
--- a/lib/fake_matrix_api.dart
+++ b/lib/fake_matrix_api.dart
@@ -127,10 +127,6 @@ class FakeMatrixApi extends BaseClient {
 
     //print('\$method request to $action with Data: $data');
 
-    // Sync requests with timeout
-    if (data is Map<String, dynamic> && data['timeout'] is String) {
-      await Future.delayed(Duration(seconds: 5));
-    }
     if (!servers.contains(request.url.origin)) {
       return Response(
           '<html><head></head><body>Not found ${request.url.origin}...</body></html>',
@@ -202,8 +198,19 @@ class FakeMatrixApi extends BaseClient {
               '/client/v3/rooms/!1234%3AfakeServer.notExisting/state/')) {
         res = {'event_id': '\$event${_eventCounter++}'};
       } else if (action.contains('/client/v3/sync')) {
+        // Sync requests with timeout
+        final timeout = request.url.queryParameters['timeout'];
+        if (timeout != null && timeout != '0') {
+          await Future.delayed(Duration(milliseconds: 50));
+        }
         res = {
-          'next_batch': DateTime.now().millisecondsSinceEpoch.toString(),
+          // So that it is clear which sync we are processing prefix it with 'empty_'
+          'next_batch': 'empty_${DateTime.now().millisecondsSinceEpoch}',
+          // ensure we don't generate new keys for no reason
+          'device_one_time_keys_count': {
+            'curve25519': 10,
+            'signed_curve25519': 100
+          },
         };
       } else if (method == 'PUT' &&
           _client != null &&
@@ -1037,7 +1044,7 @@ class FakeMatrixApi extends BaseClient {
         '@bob:example.com',
       ],
     },
-    'device_one_time_keys_count': {'curve25519': 10, 'signed_curve25519': 20},
+    'device_one_time_keys_count': {'curve25519': 10, 'signed_curve25519': 100},
   };
 
   static Map<String, dynamic> archiveSyncResponse = {
diff --git a/test/calls_test.dart b/test/calls_test.dart
index 7ecbace7..2e3c4372 100644
--- a/test/calls_test.dart
+++ b/test/calls_test.dart
@@ -16,6 +16,7 @@ void main() {
     Logs().level = Level.info;
     setUp(() async {
       matrix = await getClient();
+      await matrix.abortSync();
 
       voip = VoIP(matrix, MockWebRTCDelegate());
       VoIP.customTxid = '1234';
diff --git a/test/client_test.dart b/test/client_test.dart
index 461f43c7..55445635 100644
--- a/test/client_test.dart
+++ b/test/client_test.dart
@@ -45,11 +45,13 @@ void main() {
     final dbPath = join(Directory.current.path, 'test.sqlite');
 
     setUp(() async {
-      expect(await File(dbPath).exists(), false);
+      expect(await File(dbPath).exists(), false,
+          reason: '$dbPath should not exist');
       clientOnPath = await getClient(
         databasePath: dbPath,
       );
-      expect(await File(dbPath).exists(), true);
+      await clientOnPath.abortSync();
+      expect(await File(dbPath).exists(), true, reason: '$dbPath should exist');
     });
     test('logout', () async {
       expect(await File(dbPath).exists(), true);
@@ -137,11 +139,12 @@ void main() {
         newOlmAccount: pickledOlmAccount,
       );
 
-      await Future.delayed(Duration(milliseconds: 50));
-
       final loginState = await loginStateFuture;
       final sync = await syncFuture;
 
+      // to ensure our state doesn't get overwritten once we manually inject SyncUpdates
+      await matrix.abortSync();
+
       expect(loginState, LoginState.loggedIn);
       expect(matrix.onSync.value != null, true);
       expect(matrix.encryptionEnabled, true);
@@ -185,7 +188,7 @@ void main() {
           PresenceType.online);
       expect(presenceCounter, 1);
       expect(accountDataCounter, 10);
-      await Future.delayed(Duration(milliseconds: 50));
+
       expect(matrix.userDeviceKeys.keys.toSet(), {
         '@alice:example.com',
         '@othertest:fakeServer.notExisting',
@@ -1134,7 +1137,7 @@ void main() {
         newOlmAccount: pickledOlmAccount,
       );
 
-      await Future.delayed(Duration(milliseconds: 500));
+      await client1.abortSync();
 
       expect(client1.isLogged(), true);
       expect(client1.rooms.length, 3);
@@ -1146,7 +1149,8 @@ void main() {
       );
 
       await client2.init();
-      await Future.delayed(Duration(milliseconds: 500));
+
+      await client2.abortSync();
 
       expect(client2.isLogged(), true);
       expect(client2.accessToken, client1.accessToken);
@@ -1197,6 +1201,7 @@ void main() {
       await client.getWellknown();
       expect(
           client.wellKnown?.mHomeserver.baseUrl.host, 'fakeserver.notexisting');
+      await client.dispose();
     });
 
     test('refreshAccessToken', () async {
@@ -1204,6 +1209,7 @@ void main() {
       expect(client.accessToken, 'abcd');
       await client.refreshAccessToken();
       expect(client.accessToken, 'a_new_token');
+      await client.dispose();
     });
 
     test('handleSoftLogout', () async {
@@ -1226,6 +1232,7 @@ void main() {
         storedClient?.tryGet<String>('refresh_token'),
         'another_new_token',
       );
+      await client.dispose();
     });
 
     test('object equality', () async {
@@ -1274,6 +1281,7 @@ void main() {
       final client = await getClient();
       client.backgroundSync = true;
       await client.clearCache();
+      await client.dispose();
     });
 
     test('dispose', () async {
@@ -1311,6 +1319,7 @@ void main() {
       await hiveClient.init();
       await Future.delayed(Duration(milliseconds: 200));
       expect(hiveClient.isLogged(), true);
+      await hiveClient.dispose(closeDatabase: false);
     });
 
     test('getEventByPushNotification', () async {
@@ -1402,6 +1411,8 @@ void main() {
               null,
           true,
           reason: '!5345234235:example.com not found as archived room');
+
+      await client.dispose();
     });
 
     test(
@@ -1430,6 +1441,7 @@ void main() {
           expect(error.userId, '@user:server');
           expect(error.toString(), 'Exception: BAD_ACCOUNT_KEY');
         }
+        await customClient.dispose(closeDatabase: true);
       },
     );
 
diff --git a/test/device_keys_list_test.dart b/test/device_keys_list_test.dart
index c0663d7b..3332aa74 100644
--- a/test/device_keys_list_test.dart
+++ b/test/device_keys_list_test.dart
@@ -32,6 +32,7 @@ void main() {
 
     test('setupClient', () async {
       client = await getClient();
+      await client.abortSync();
     });
 
     test('fromJson', () async {
diff --git a/test/encryption/cross_signing_test.dart b/test/encryption/cross_signing_test.dart
index 8ac7178b..43592edd 100644
--- a/test/encryption/cross_signing_test.dart
+++ b/test/encryption/cross_signing_test.dart
@@ -34,6 +34,7 @@ void main() {
       await olm.init();
       olm.get_library_version();
       client = await getClient();
+      await client.abortSync();
     });
 
     test('basic things', () async {
diff --git a/test/encryption/key_request_test.dart b/test/encryption/key_request_test.dart
index 307aee7b..4fe24e66 100644
--- a/test/encryption/key_request_test.dart
+++ b/test/encryption/key_request_test.dart
@@ -76,6 +76,8 @@ void main() {
     });
     test('Reply To Request', () async {
       final matrix = await getClient();
+      await matrix.abortSync();
+
       matrix.setUserId('@alice:example.com'); // we need to pretend to be alice
       FakeMatrixApi.calledEndpoints.clear();
       await matrix
diff --git a/test/encryption/key_verification_test.dart b/test/encryption/key_verification_test.dart
index 8bfdea0a..76676203 100644
--- a/test/encryption/key_verification_test.dart
+++ b/test/encryption/key_verification_test.dart
@@ -95,8 +95,13 @@ void main() async {
         KeyVerificationMethod.reciprocate
       };
 
+      // cancel sync to reduce background load and prevent sync overwriting which keys are tracked.
+      await client1.abortSync();
+      await client2.abortSync();
+
       // get client2 device keys to start verification
       await client1.updateUserDeviceKeys(additionalUsers: {client2.userID!});
+      await client2.updateUserDeviceKeys(additionalUsers: {client1.userID!});
     });
 
     tearDown(() async {
diff --git a/test/fake_client.dart b/test/fake_client.dart
index 42911fe5..fcf46da4 100644
--- a/test/fake_client.dart
+++ b/test/fake_client.dart
@@ -53,6 +53,7 @@ Future<Client> getClient({
     newOlmAccount: pickledOlmAccount,
   );
   await Future.delayed(Duration(milliseconds: 10));
+  await client.abortSync();
   return client;
 }
 
diff --git a/test/room_test.dart b/test/room_test.dart
index 3e08e2cc..3854dcb1 100644
--- a/test/room_test.dart
+++ b/test/room_test.dart
@@ -55,6 +55,7 @@ void main() {
     Logs().level = Level.error;
     test('Login', () async {
       matrix = await getClient();
+      await matrix.abortSync();
     });
 
     test('Create from json', () async {
diff --git a/test/timeline_test.dart b/test/timeline_test.dart
index 5421dcf7..e87a1144 100644
--- a/test/timeline_test.dart
+++ b/test/timeline_test.dart
@@ -67,6 +67,7 @@ void main() {
       client = await getClient(
         sendTimelineEventTimeout: const Duration(seconds: 5),
       );
+      await client.abortSync();
 
       final poison = Random().nextInt(2 ^ 32);
       currentPoison = poison;
diff --git a/test/user_test.dart b/test/user_test.dart
index 309cacb4..85d51f90 100644
--- a/test/user_test.dart
+++ b/test/user_test.dart
@@ -48,6 +48,7 @@ void main() {
       await client.login(LoginType.mLoginPassword,
           identifier: AuthenticationUserIdentifier(user: 'test'),
           password: '1234');
+      await client.abortSync();
     });
     tearDown(() async {
       await client.logout();