Ich habe gesteren dieses Link von "Breland11" gefunden und könnte heute morgen problemlos Radio zuhören - vielleicht war nur ein Zufall :).
Car Play will always try and take priority over the cars selected mode if it is the first connection made upon starting up. Therefore, at the end of a journey, disconnect your phone first and put your car into radio mode. When you get back into your car, start up with the car still in radio mode 'then' connect your phone, at the end of the sequence. The poster suggests this will prioritise your cars system over Car Play. Car Play will still work when called upon but will not keep assuming priority.