Just bought a TCL 55R635 TV and noticed that the Amazon Music app breaks audio output for the entire TV if you launch the Amazon Music app first (TCL eARC -> Pioneer ARC). If you open a non-Amazon Music app first and then open Amazon Music, audio plays fine. Also, if you turn off the TV and back on after a bit and launch Amazon Music first, again no audio. Only fix is to restart the TV.
Since we have a Nvidia Shield and the Roku Amazon Music doesn't support HD/Ultra HD (which Shield does), I'll just uninstall the app for now. I doubt we'll use the Roku interface much anyway, since Roku won't pay for a MPEG license (which Channels DVR requires) anyway. Maybe when watching Disney+ or if we upgrade to Netflix 4k (since I have the 2017 Shield which doesn't support Dolby Vision (only the 2019 model does)).