Bluetooth Serial Port Profile (SPP) Devices not discovered by modified btchat@Android

I like to discover SPP with my Android application.
This is not working.

So I did some tests with btchat:
...
RemoteSelector remoteSelector(adapter);
//remoteSelector.startDiscovery(QBluetoothUuid(serviceUuid)); // => origional code
//remoteSelector.startDiscovery(QBluetoothUuid(QBluetoothUuid::SerialPort)); // => this should discover all SPP devices => not working
remoteSelector.startDiscovery(QBluetoothUuid()); // => this should discover any device => my PC is listed => so BT is working in general
if (remoteSelector.exec() == QDialog::Accepted) {
...