Within the last few weeks, my AppleTV (not 4K) upgraded to the new version of the app. The layout changed to the left bar. It seems like since around the time of this upgrade, performance of the GUI is not good. Not sure if I noticed it initially though. Anyhow, when going into Channels from the AppleTV launcher, it seems to take quite some time before the application is responsive. I can push buttons on the remote, but nothing happens for a while. Finally, after a bit, it seems like my button presses show up on the screen. I think I've seen other slowness in the GUI as well. Something else I've noticed is that it seems as if playback isn't always smooth now. I was watching a show recently and it was panning down, I believe, and it kept glitching occasionally. It's possible that was the source, but I believe I"ve noticed similar glitches on other recordings as well.
I'm using the Docker version of the DVR software (2020.06.16.1927). I don't recall when I got upgraded to the new AppleTV version (last few weeks?). My AppleTV is hard wired, not on wireless (unless something has changed, unknown to me - I can validate and post back if it has moved to Wifi for some reason).
Oh, and the interface on my iPhone is fine. It does give me a message when starting the app (Preparing your TV) for a few seconds, then changes to Loading, and almost immediately then shows up my library.