Was excited this morning to see that the latest 15.2 beta was being reported as fixing the 'left channel only' problem for Dolby Atmos and Dolby Audio that has been around for the last two odd months on Apple Music on Apple TV 4K. With some trepidation, I decided to update this morning, only to also find the 'Get Beta Updates' option was missing, as others had reported. I was still on 15.0, so I decided to update to 15.1.1 hoping the Beta option would appear. No luck. As before the 'left channel' issue was still there and no Beta option. The scrollback 'fix?' still worked, so no worse off.
This afternoon the Beta option reappeared, so I took the plunge. It seemed to take a long time compared to this mornings updates, but eventually, the main screen reappeared. There was a moment of panic, when, after a bit of testing, the 'left channel issue' was still there and no amount of back or forward scrolling made any difference and the other speakers stayed dead. After googling 'How to remove the beta?' and 'How to throw your Apple TV out the window', I rebooted the box by removing the power cable for a few minutes (which was the solution on earlier Apple TV's, after Steve Jobs had insisted on no power button) and then restarting it. Since then, everything I've tested is playing correctly and it will play without complaint between Dolby Atmos, Dolby Audio and Lossless. I guess it's possible some sort of restart might upset it but for the moment all seems stable.
Now we can wait for the Hi-Res update that I understood was due late in the year and see if that can really stuff it up. For the moment I'm happy, although I will leave the unaffected 14.7 units alone, till the final version of 15.2 becomes available. I would suggest doing the same if you still have 14.7. Its not unknown for a later Beta to mess something up. If you have 15.0 or up and want to consider the beta, thats my experience so far.
Thanks for the news of the 'working' beta this morning. Made my day.
Thanks for that detailed report!