SDP registration is not possible per local adapter.

QBluetoothServiceInfo::registerService(const QBluetoothAddress &localAdapter = QBluetoothAddress());

The localAdapter parameter is ignored on Bluez5. The relevant Bluez5 DBus API registers the current service object on all devices despite the fact that the server is only running on one adapter.

Unfortunately the Bluez5 DBus API does not offer the option to choose the local adapter. Fixing this would require to manually interact with the SDP server which is a lot of effort. The question is whether two local devices are a use case that needs to be covered...