Not carplay related (my car is too old), but we've been having an odd audio issue with my wife's iPhone 12 with iOS 15... when connected to my car stereo via USB the Music app plays fine, but if we try to play anything from the Audible app then as soon as the phone locks the audio gets muted. The car stereo shows as still playing - i.e. track time keeps advancing - but there is no sound coming from the speakers. Unlock the phone and the audio comes back.