Mediasystem Plus -> Problems with Android Auto?!

I always have difficulty playing my music (spotify) over Android Auto. A good USB cable and a Samsung Galaxy A 3 (2017) are used. The mobile phone is also recognized spontaneously. I can operate Android Auto normally. The selected track also runs (see the charging bar) but there is no sound to hear. Then there are days when everything works fine and the songs can be played quite normally, i.e. also music can be heard. Switch to Original-La dekabel doesn’t work either, i.e. everything is great, sometimes no sound to hear. What am I doing wrong? I’m not the mobile/multimedia expert now. Did anyone ever do that? Do you open Android car separately on your mobile phone before connecting to the USB port in Ibiza? How satisfied are you with Android car or Full Link as such? My initial skepticism has already come true here. You freckles about it more than one person is fond of and recommend when driving a car. It’s worth it… it’s got a lot of gambling on the whole.