diff --git a/lib/src/services/api.service.dart b/lib/src/services/api.service.dart
index a78e709e..70e51353 100644
--- a/lib/src/services/api.service.dart
+++ b/lib/src/services/api.service.dart
@@ -35,6 +35,7 @@ import 'package:twonly/src/services/group.services.dart';
 import 'package:twonly/src/services/notifications/fcm.notifications.dart';
 import 'package:twonly/src/services/notifications/pushkeys.notifications.dart';
 import 'package:twonly/src/services/signal/identity.signal.dart';
+import 'package:twonly/src/services/signal/protocol_state.signal.dart';
 import 'package:twonly/src/services/signal/utils.signal.dart';
 import 'package:twonly/src/services/subscription.service.dart';
 import 'package:twonly/src/services/user.service.dart';
@@ -121,6 +122,7 @@ class ApiService {
       unawaited(syncFlameCounters());
       unawaited(setupNotificationWithUsers());
       unawaited(signalHandleNewServerConnection());
+      resetResyncedUsers();
       unawaited(fetchGroupStatesForUnjoinedGroups());
       unawaited(fetchMissingGroupPublicKey());
       unawaited(checkForDeletedUsernames());
diff --git a/lib/src/services/api/client2client/errors.c2c.dart b/lib/src/services/api/client2client/errors.c2c.dart
index 5b8093f1..bc03adfd 100644
--- a/lib/src/services/api/client2client/errors.c2c.dart
+++ b/lib/src/services/api/client2client/errors.c2c.dart
@@ -26,6 +26,8 @@ Future<void> handleErrorMessage(
           requested: Value(true),
         ),
       );
+    case EncryptedContent_ErrorMessages_Type.SESSION_OUT_OF_SYNC:
+      break; // The other user initiated a new signal session, so ignore the error in this case, as the new session works...
     // ignore: no_default_cases
     default:
       break;
diff --git a/lib/src/services/api/server_messages.api.dart b/lib/src/services/api/server_messages.api.dart
index 46dfd569..a94f9b6e 100644
--- a/lib/src/services/api/server_messages.api.dart
+++ b/lib/src/services/api/server_messages.api.dart
@@ -74,7 +74,6 @@ Future<void> handleServerMessage(server.ServerToClient msg) async {
 }
 
 DateTime lastPushKeyRequest = clock.now().subtract(const Duration(hours: 1));
-bool alreadyPerformedAnResync = false;
 
 Mutex protectReceiptCheck = Mutex();
 
diff --git a/lib/src/services/signal/encryption.signal.dart b/lib/src/services/signal/encryption.signal.dart
index e9faaaab..96aee2b5 100644
--- a/lib/src/services/signal/encryption.signal.dart
+++ b/lib/src/services/signal/encryption.signal.dart
@@ -3,21 +3,18 @@ import 'dart:typed_data';
 import 'package:libsignal_protocol_dart/libsignal_protocol_dart.dart';
 // ignore: implementation_imports
 import 'package:libsignal_protocol_dart/src/invalid_message_exception.dart';
-import 'package:mutex/mutex.dart';
 import 'package:twonly/src/model/protobuf/client/generated/messages.pb.dart';
 import 'package:twonly/src/services/api/messages.api.dart';
+import 'package:twonly/src/services/signal/protocol_state.signal.dart';
 import 'package:twonly/src/services/signal/session.signal.dart';
 import 'package:twonly/src/services/signal/utils.signal.dart';
 import 'package:twonly/src/utils/log.dart';
 
-/// This caused some troubles, so protection the encryption...
-final lockingSignalEncryption = Mutex();
-
 Future<CiphertextMessage?> signalEncryptMessage(
   int target,
   Uint8List plaintextContent,
 ) async {
-  return lockingSignalEncryption.protect<CiphertextMessage?>(() async {
+  return lockingSignalProtocol.protect<CiphertextMessage?>(() async {
     try {
       final signalStore = (await getSignalStore())!;
       final address = getSignalAddress(target);
@@ -30,62 +27,62 @@ Future<CiphertextMessage?> signalEncryptMessage(
   });
 }
 
-bool alreadyPerformedAnResync = false;
-
 Future<(EncryptedContent?, PlaintextContent_DecryptionErrorMessage_Type?)>
 signalDecryptMessage(
   int fromUserId,
   Uint8List encryptedContentRaw,
   int type,
 ) async {
-  try {
-    final session = SessionCipher.fromStore(
-      (await getSignalStore())!,
-      getSignalAddress(fromUserId),
-    );
+  return lockingSignalProtocol.protect(() async {
+    try {
+      final session = SessionCipher.fromStore(
+        (await getSignalStore())!,
+        getSignalAddress(fromUserId),
+      );
 
-    Uint8List plaintext;
+      Uint8List plaintext;
 
-    switch (type) {
-      case CiphertextMessage.prekeyType:
-        plaintext = await session.decrypt(
-          PreKeySignalMessage(encryptedContentRaw),
-        );
-      case CiphertextMessage.whisperType:
-        plaintext = await session.decryptFromSignal(
-          SignalMessage.fromSerialized(encryptedContentRaw),
-        );
-      default:
-        Log.error('Unknown Message Decryption Type: $type');
-        return (null, PlaintextContent_DecryptionErrorMessage_Type.UNKNOWN);
-    }
-
-    return (EncryptedContent.fromBuffer(plaintext), null);
-  } on InvalidKeyIdException catch (e) {
-    Log.warn(e);
-    return (null, PlaintextContent_DecryptionErrorMessage_Type.PREKEY_UNKNOWN);
-  } on InvalidMessageException catch (e) {
-    if (!alreadyPerformedAnResync) {
-      if (await handleSessionResync(fromUserId)) {
-        // This flag prevents from resyncing the session the client received multiple new
-        // messages from the server he could not decrypt
-        alreadyPerformedAnResync = true;
-
-        // This message contains a new PreKeyBundle establishing a new signal session
-        await sendCipherText(
-          fromUserId,
-          EncryptedContent(
-            errorMessages: EncryptedContent_ErrorMessages(
-              type: EncryptedContent_ErrorMessages_Type.SESSION_OUT_OF_SYNC,
-            ),
-          ),
-        );
+      switch (type) {
+        case CiphertextMessage.prekeyType:
+          plaintext = await session.decrypt(
+            PreKeySignalMessage(encryptedContentRaw),
+          );
+        case CiphertextMessage.whisperType:
+          plaintext = await session.decryptFromSignal(
+            SignalMessage.fromSerialized(encryptedContentRaw),
+          );
+        default:
+          Log.error('Unknown Message Decryption Type: $type');
+          return (null, PlaintextContent_DecryptionErrorMessage_Type.UNKNOWN);
       }
+
+      return (EncryptedContent.fromBuffer(plaintext), null);
+    } on InvalidKeyIdException catch (e) {
+      Log.warn(e);
+      return (null, PlaintextContent_DecryptionErrorMessage_Type.PREKEY_UNKNOWN);
+    } on InvalidMessageException catch (e) {
+      if (!resyncedUsers.contains(fromUserId)) {
+        if (await handleSessionResync(fromUserId)) {
+          // This flag prevents from resyncing the session the client received multiple new
+          // messages from the server he could not decrypt
+          resyncedUsers.add(fromUserId);
+
+          // This message contains a new PreKeyBundle establishing a new signal session
+          await sendCipherText(
+            fromUserId,
+            EncryptedContent(
+              errorMessages: EncryptedContent_ErrorMessages(
+                type: EncryptedContent_ErrorMessages_Type.SESSION_OUT_OF_SYNC,
+              ),
+            ),
+          );
+        }
+      }
+      Log.warn(e);
+      return (null, PlaintextContent_DecryptionErrorMessage_Type.UNKNOWN);
+    } catch (e) {
+      Log.error(e);
+      return (null, PlaintextContent_DecryptionErrorMessage_Type.UNKNOWN);
     }
-    Log.warn(e);
-    return (null, PlaintextContent_DecryptionErrorMessage_Type.UNKNOWN);
-  } catch (e) {
-    Log.error(e);
-    return (null, PlaintextContent_DecryptionErrorMessage_Type.UNKNOWN);
-  }
+  });
 }
diff --git a/lib/src/services/signal/identity.signal.dart b/lib/src/services/signal/identity.signal.dart
index a257e0fc..bb053c2c 100644
--- a/lib/src/services/signal/identity.signal.dart
+++ b/lib/src/services/signal/identity.signal.dart
@@ -9,6 +9,7 @@ import 'package:twonly/src/constants/secure_storage.keys.dart';
 import 'package:twonly/src/database/signal/signal_protocol_store.dart';
 import 'package:twonly/src/model/json/signal_identity.model.dart';
 import 'package:twonly/src/services/signal/consts.signal.dart';
+import 'package:twonly/src/services/signal/protocol_state.signal.dart';
 import 'package:twonly/src/services/signal/utils.signal.dart';
 import 'package:twonly/src/services/user.service.dart';
 import 'package:twonly/src/utils/log.dart';
@@ -57,21 +58,23 @@ Future<void> signalHandleNewServerConnection() async {
 }
 
 Future<List<PreKeyRecord>> signalGetPreKeys() async {
-  final user = await getUser();
-  if (user == null) return [];
+  return lockingSignalProtocol.protect(() async {
+    final user = await getUser();
+    if (user == null) return [];
 
-  final start = user.currentPreKeyIndexStart;
-  await updateUser((user) {
-    user.currentPreKeyIndexStart =
-        (user.currentPreKeyIndexStart + 200) % maxValue;
+    final start = user.currentPreKeyIndexStart;
+    await updateUser((user) {
+      user.currentPreKeyIndexStart =
+          (user.currentPreKeyIndexStart + 200) % maxValue;
+    });
+    final preKeys = generatePreKeys(start, 200);
+    final signalStore = await getSignalStore();
+    if (signalStore == null) return [];
+    for (final p in preKeys) {
+      await signalStore.preKeyStore.storePreKey(p.id, p);
+    }
+    return preKeys;
   });
-  final preKeys = generatePreKeys(start, 200);
-  final signalStore = await getSignalStore();
-  if (signalStore == null) return [];
-  for (final p in preKeys) {
-    await signalStore.preKeyStore.storePreKey(p.id, p);
-  }
-  return preKeys;
 }
 
 Future<SignalIdentity?> getSignalIdentity() async {
@@ -136,26 +139,28 @@ Future<void> createIfNotExistsSignalIdentity() async {
 }
 
 Future<SignedPreKeyRecord?> _getNewSignalSignedPreKey() async {
-  var identityKeyPair = await getSignalIdentityKeyPair();
-  final user = await getUser();
-  final signalStore = await getSignalStore();
-  if (identityKeyPair == null || signalStore == null || user == null) {
-    return null;
-  }
+  return lockingSignalProtocol.protect(() async {
+    var identityKeyPair = await getSignalIdentityKeyPair();
+    final user = await getUser();
+    final signalStore = await getSignalStore();
+    if (identityKeyPair == null || signalStore == null || user == null) {
+      return null;
+    }
 
-  final signedPreKeyId = user.currentSignedPreKeyIndexStart;
-  await updateUser((user) {
-    user.currentSignedPreKeyIndexStart += 1;
+    final signedPreKeyId = user.currentSignedPreKeyIndexStart;
+    await updateUser((user) {
+      user.currentSignedPreKeyIndexStart += 1;
+    });
+
+    final signedPreKey = generateSignedPreKey(
+      identityKeyPair,
+      signedPreKeyId,
+    );
+
+    identityKeyPair = null;
+
+    await signalStore.storeSignedPreKey(signedPreKeyId, signedPreKey);
+
+    return signedPreKey;
   });
-
-  final signedPreKey = generateSignedPreKey(
-    identityKeyPair,
-    signedPreKeyId,
-  );
-
-  identityKeyPair = null;
-
-  await signalStore.storeSignedPreKey(signedPreKeyId, signedPreKey);
-
-  return signedPreKey;
 }
diff --git a/lib/src/services/signal/protocol_state.signal.dart b/lib/src/services/signal/protocol_state.signal.dart
new file mode 100644
index 00000000..9d797473
--- /dev/null
+++ b/lib/src/services/signal/protocol_state.signal.dart
@@ -0,0 +1,12 @@
+import 'package:mutex/mutex.dart';
+
+/// Unified lock for all Signal protocol operations (encryption, decryption, session management).
+final lockingSignalProtocol = Mutex();
+
+/// Tracking users who have already been resynced in the current session.
+final resyncedUsers = <int>{};
+
+/// Reset the resync tracking set.
+void resetResyncedUsers() {
+  resyncedUsers.clear();
+}
diff --git a/lib/src/services/signal/session.signal.dart b/lib/src/services/signal/session.signal.dart
index 804adc00..03554d32 100644
--- a/lib/src/services/signal/session.signal.dart
+++ b/lib/src/services/signal/session.signal.dart
@@ -4,81 +4,77 @@ import 'package:libsignal_protocol_dart/libsignal_protocol_dart.dart';
 import 'package:twonly/locator.dart';
 import 'package:twonly/src/model/protobuf/api/websocket/server_to_client.pb.dart';
 import 'package:twonly/src/services/signal/consts.signal.dart';
+import 'package:twonly/src/services/signal/protocol_state.signal.dart';
 import 'package:twonly/src/services/signal/utils.signal.dart';
 import 'package:twonly/src/utils/log.dart';
 
 Future<bool> processSignalUserData(Response_UserData userData) async {
-  final SignalProtocolStore? signalStore = await getSignalStore();
+  return lockingSignalProtocol.protect(() async {
+    final SignalProtocolStore? signalStore = await getSignalStore();
 
-  if (signalStore == null) {
-    return false;
-  }
+    if (signalStore == null) {
+      return false;
+    }
 
-  final targetAddress = getSignalAddress(userData.userId.toInt());
+    final targetAddress = getSignalAddress(userData.userId.toInt());
 
-  final sessionBuilder = SessionBuilder.fromSignalStore(
-    signalStore,
-    targetAddress,
-  );
+    final sessionBuilder = SessionBuilder.fromSignalStore(
+      signalStore,
+      targetAddress,
+    );
 
-  ECPublicKey? tempPrePublicKey;
-  int? tempPreKeyId;
+    ECPublicKey? tempPrePublicKey;
+    int? tempPreKeyId;
 
-  if (userData.prekeys.isNotEmpty) {
-    tempPrePublicKey = Curve.decodePoint(
-      DjbECPublicKey(
-        Uint8List.fromList(userData.prekeys.first.prekey),
-      ).serialize(),
+    if (userData.prekeys.isNotEmpty) {
+      tempPrePublicKey = Curve.decodePoint(
+        DjbECPublicKey(
+          Uint8List.fromList(userData.prekeys.first.prekey),
+        ).serialize(),
+        1,
+      );
+      tempPreKeyId = userData.prekeys.first.id.toInt();
+    }
+
+    final tempSignedPreKeyId = userData.signedPrekeyId.toInt();
+
+    final tempSignedPreKeyPublic = Curve.decodePoint(
+      DjbECPublicKey(Uint8List.fromList(userData.signedPrekey)).serialize(),
       1,
     );
-    tempPreKeyId = userData.prekeys.first.id.toInt();
-  }
 
-  final tempSignedPreKeyId = userData.signedPrekeyId.toInt();
+    final tempSignedPreKeySignature = Uint8List.fromList(
+      userData.signedPrekeySignature,
+    );
 
-  final tempSignedPreKeyPublic = Curve.decodePoint(
-    DjbECPublicKey(Uint8List.fromList(userData.signedPrekey)).serialize(),
-    1,
-  );
+    final tempIdentityKey = IdentityKey(
+      Curve.decodePoint(
+        DjbECPublicKey(
+          Uint8List.fromList(userData.publicIdentityKey),
+        ).serialize(),
+        1,
+      ),
+    );
 
-  final tempSignedPreKeySignature = Uint8List.fromList(
-    userData.signedPrekeySignature,
-  );
+    final preKeyBundle = PreKeyBundle(
+      userData.registrationId.toInt(),
+      defaultDeviceId,
+      tempPreKeyId,
+      tempPrePublicKey,
+      tempSignedPreKeyId,
+      tempSignedPreKeyPublic,
+      tempSignedPreKeySignature,
+      tempIdentityKey,
+    );
 
-  final tempIdentityKey = IdentityKey(
-    Curve.decodePoint(
-      DjbECPublicKey(
-        Uint8List.fromList(userData.publicIdentityKey),
-      ).serialize(),
-      1,
-    ),
-  );
-
-  final preKeyBundle = PreKeyBundle(
-    userData.registrationId.toInt(),
-    defaultDeviceId,
-    tempPreKeyId,
-    tempPrePublicKey,
-    tempSignedPreKeyId,
-    tempSignedPreKeyPublic,
-    tempSignedPreKeySignature,
-    tempIdentityKey,
-  );
-
-  try {
-    await sessionBuilder.processPreKeyBundle(preKeyBundle);
-    return true;
-  } catch (e) {
-    Log.error('could not process pre key bundle: $e');
-    return false;
-  }
-}
-
-Future<void> deleteSessionWithTarget(int target) async {
-  final signalStore = await getSignalStore();
-  if (signalStore == null) return;
-  final address = SignalProtocolAddress(target.toString(), defaultDeviceId);
-  await signalStore.sessionStore.deleteSession(address);
+    try {
+      await sessionBuilder.processPreKeyBundle(preKeyBundle);
+      return true;
+    } catch (e) {
+      Log.error('could not process pre key bundle: $e');
+      return false;
+    }
+  });
 }
 
 Future<Uint8List?> getPublicKeyFromContact(int contactId) async {