i have a Samsung Galaxy S6 and 2015 Mazda. In general, access my music via bluetooth in my car works much better when I disable Google PLay Music and only use the native music app. However, I would prefer to use Google Play Music simply because when I purchase music from the app and download them to the phone, they are not available to the native app (or any app other than Google Play music...argh!)
So, I am using Tasker to successfully automatically play Google Play Music when it connects to the car's bluetooth, and that works very well. And the music does play.
However, and this is my specific problem, sometimes I cannot access the library screen on my cars bluetooth system, where I choose the artist, track, playlist, album, etc.
Specifically, when I try to select the library icon, it says: "unable to view the content of the connected device."
Sometimes this works, sometimes it doesn't.