I'm having the same issue. It's just very recent, so I think it has to do with the 14.7 update. I've tested it similarly to the original poster. It is NOT App related. All audio is out of sync, not just a particular app, it's the interface too. Every little beep of the home screen navigation is delayed. So far, I have tried:
- Restarting
- Resetting
- Two different HDMI cables
- Two different HDMI ports on my TV
- Sync issue affects all apps - Netflix, YouTube, Hulu, Amazon, Crunchyroll, Twitch, etc.
- Closing all the apps (as one poster recommended) did not help
- My TV's built in apps play audio in sync
- My Playstation plays audio in sync
The only thing that seems to work is to unplug it from both the power and HDMI and just let it sit awhile. Then it's back in sync for maybe half a day to a day and then it's time to repeat the exercise again.
It has to be an AppleTV software issue.
Thanks.