Apple Car Play has just stopped working in my car. The head unit still ‘sees’ my phone as a source to play music from in media, but it won’t see it in the app. I’ve tried different cables and phones with no luck. 
 

Can anyone suggest anything to try or is it a dealer visit. Who will no doubt blame the phone. 

Try unlocking the phone whilst it's connected up and 'app' is selected?

Tried that. Tried forgetting the car in the iPhone. Tried a factory reset on the infotainment system as well. 

mine sometimes does it. Do you get the phone signal bars?

 

A solution may have presented itself. 
 

the USB media source isn’t working now. Maybe the socket is FUBARd. 

Try a new/different phone cable