no more communications when I negotiate the MTU

Question

From the Flutter app, the ble peripheral (I use flutter_blue_plus) communicate with my central (an ESP32). As I want to increase the MTU to the maximum 512b.

But for some reasons I don't understand, the communication with the central does not work. If I comment the call to bleNegotiateMtu(device), it works back again.

The result is as expected (see logs at the bottom):

I/flutter ( 6165): Connected!
I/flutter ( 6165): Initial MTU is 20 bytes. Try to negotiate 512 bytes…
D/BluetoothGatt( 6165): configureMTU() - device: 34:94:54:47:CE:XX mtu: 512
I/flutter ( 6165): Final negociated MTU is 512 bytes.

Any idea?

  /// Negotiate MTU
  void bleNegotiateMtu(BluetoothDevice device) async {
    // == Get current MTU
    int mtu = await device.mtu.first;
    print("Initial MTU is $mtu bytes. Try to negotiate 512 bytes…");
    // == Negociate 512b MTU
    mtu = await device.requestMtu(512);
    print("Final negociated MTU is $mtu bytes.");
  }

    /// Connect to the device or, if already connected, show the details screen
    final onPressConnect = () async {
      try {
        setState(() {
          _connectingDevice = device;
          _connecting = true;
          _error = null;
        });

        stopScan();

        debugPrint('Connecting to the device…');
        final future = device.connect();

        debugPrint("Create cancelable future");
        _cancelableOperation = CancelableOperation.fromFuture(
          future,
          onCancel: () {
            debugPrint('onCancel');
            setState(() {
              _connectingDevice = null;
              _connecting = false;
              _error = null;
            });
          },
        );

        debugPrint("Attaching future resolve");
        future.then((arg) {
          debugPrint("Connected!");

          setState(() {
            _connecting = false;
            _connectedDevice = device;
          });

          // == Negotiate MTU
          bleNegotiateMtu(device);

          Navigator.push(context, MaterialPageRoute(builder: (context) {
            // == Display the right dashboard
            // = Smartbox dashboard
            if (isSmartbox) return SmartboxDashboard(device: device);

            // == Unknown generic ble device
            return Dashboard(device: device);
          }));
        }).catchError((e) {
          print("error $e");
          _error = e;
        });
      } catch (e) {
        print('Connection error $e');

        // if (e.code != 'already_connected') {
        //   print('Aleady disconnected!');
        //   throw e;
        // }
        _error = e;
      } finally {}
    };

[UPDATE] Here are the log I get:

/flutter ( 6165): Currently not scaning…
D/BluetoothGatt( 6165): onClientConnectionState() - status=0 clientIf=10 device=34:94:54:47:CE:XX
D/FlutterBluePlugin( 6165): [onConnectionStateChange] status: 0 newState: 2
I/flutter ( 6165): Connected!
I/flutter ( 6165): Initial MTU is 20 bytes. Try to negotiate 512 bytes…
D/BluetoothGatt( 6165): configureMTU() - device: 34:94:54:47:CE:XX mtu: 512
I/flutter ( 6165):  Dashboard: Discovering the services from initState()
I/flutter ( 6165):  Dashboard: discoverServices(): Discovering services
I/flutter ( 6165): Currently not scaning…
D/BluetoothManager( 6165): getConnectionState()
D/BluetoothManager( 6165): getConnectedDevices
D/BluetoothManager( 6165): getConnectionState()
D/BluetoothManager( 6165): getConnectedDevices
I/flutter ( 6165):  Dashboard: BLE: state changed to BluetoothDeviceState.connected
D/BluetoothGatt( 6165): discoverServices() - device: 34:94:54:47:CE:XX
D/BluetoothGatt( 6165): onClientConnParamsChanged() - Device=34:94:54:47:CE:XX interval=6 status=0
D/BluetoothGatt( 6165): onConfigureMTU() - Device=34:94:54:47:CE:XX mtu=512 status=0
D/FlutterBluePlugin( 6165): [onMtuChanged] mtu: 512 status: 0
I/flutter ( 6165): Final negociated MTU is 512 bytes.
D/BluetoothGatt( 6165): onClientConnParamsChanged() - Device=34:94:54:47:CE:XX interval=39 status=0
V/InputMethodManager( 6165): Starting input: tba=android.view.inputmethod.EditorInfo@3e5e1a4 nm : com.example.olenpepsmobile ic=null
I/InputMethodManager( 6165): [IMM] startInputInner - mService.startInputOrWindowGainedFocus
D/InputTransport( 6165): Input channel constructed: fd=101
D/InputTransport( 6165): Input channel destroyed: fd=99
V/InputMethodManager( 6165): Starting input: tba=android.view.inputmethod.EditorInfo@75520d3 nm : com.example.olenpepsmobile ic=null
I/InputMethodManager( 6165): [IMM] startInputInner - mService.startInputOrWindowGainedFocus
D/InputTransport( 6165): Input channel destroyed: fd=101
D/ViewRootImpl@2be3e76[MainActivity]( 6165): MSG_RESIZED_REPORT: ci=Rect(0, 72 - 0, 0) vi=Rect(0, 0 - 0, 0) or=1
D/ViewRootImpl@2be3e76[MainActivity]( 6165): MSG_WINDOW_FOCUS_CHANGED 0
D/ViewRootImpl@2be3e76[MainActivity]( 6165): MSG_RESIZED_REPORT: ci=Rect(0, 72 - 0, 0) vi=Rect(0, 72 - 0, 0) or=1