I've been experiencing the most annoying problems with some channels being out of sync. The audio is out of sync with the picture on major networks ABC, CBS, NBC etc. Channels such as MeTV, Antenna TV etc that broadcast older shows are all in perfect sync.
I also have a (cough) Firestick 4k Max and when I switch to that streamer (begrudgingly) the audio is perfectly in sync.
I can't for the life of me figure out why this is happening. It's been an issue for months. I am on the latest beta on Test Flight, I'm also on tvOS 15.2 and using the EXPERIMENTAL audio and video decoders. However it doesn't seem to matter what decoders I choose because the issue persists. Have the developers given a higher priority to Firestick? I've paid for this app on AppleTV long before it went free and I paid AGAIN for Firestick and AGAIN for my Sony Bravia with Google TV and yet AGAIN for iPad and iPhone versions. I feel I paid enough and should be getting flawless audio on all channels in the tvOS platform.