I use this app mostly in my car with bluetooth. I am using a Nexus 5X with Android Marshmallow, though I had the same problems on Android Lollipop.
It does not always work well. When I switch to bluetooth, my phone stops playing and when I switch my car back to radio the app starts in the background (I see a notification icon).
Also the app automatically starts and stops very quick sometimes, when I am not in the car.