I don't know if this still affects my Volt, as I have gotten into the habit of connecting my iPhone after the car has fully started.To add to my original post, there are still a couple minor bugs at least affecting me for some apps through Apple Play post IOS 11.
Turns out if I connect my phone to the car via USB 'before' I start the car, then Apple Play does not show or launch. If I plug in 'after' I start the car then Apple Play appears as it should.
In my Amazon Music app via Car Play, it seems after I select my music (a playlist or a station, etc) -the now playing window appears showing the song selected - but it will say 'loading' seemingly forever. Pushing the play button does nothing. But if I then go to my phone and the Amazon Music app directly and then hit play, everything is fine and the music will play through the car audio. Not only that, but then after I can hit ff or rewind or pause and all works fine. It's just needs that sort of pump prime of my hitting play from my phone directly.