I have the same problem. iPhone X, iOS 11.1.2. When my VW connects through bluetooh with the phone, the music does not want to play, although in the spotify it is played. When I click the pause and play again, the music is distorted. It only helps to restart the application. It's really tiring ...
In addition to the song playing at double speed: when I pause the music, it will start playing automatically after a few seconds. This issue is dangerous for real.
It's randomly happening and therefore it's very difficult to reproduce. Perhaps a bit weird, but I have the idea it only happens when I'm in the car with my wife and kids. That means: a second iPhone in the car (her bluetooth not connected, but registered with the car), Family Subscription, playing from a downloaded playlist.
Spotify, please acknowledge there is a problem and start searching for a solution. Plenty of people here that are willing to help.