Right now, according to the developer of the API:
Qt gets the service from the service model by the ssid, if such a network exists, and then connects to it with the later service->doConnectService();, if such a service doesn't exist in the service model, it'll try the next connection in the list of unnamed services and keep trying until it has tried all of them or one of them accepted the connection.
But, if these things end up failing, it doesn't do much to report errors.

It is sort of a flaw since at least a signal should be emitted to show an error happening.