I had the exact same problem. Even got that if I pressed a volume button once, it somehow kept going. Got me scared a few times when my volume went way up real quickly without realizing why haha. But since tvOS it looks it got solved for me though.
Edit: I Spoke too soon. Still having troubles. Weird thing is that I noticed that after a few minutes (after turning ATV on) it gets more responsive and just acts normal This was also the case on tvOS 14. So how, and why is this happening??