tvOS 15.5 dropped, although I am not optimistic for any fixes.
So, experienced something odd the other day. Was watching some Netflix content the other night (DV/DA, though I have Atmos disabled in the ATV so I'm not bothered with the popping), and was getting these brief video stutters (have seen this before, frequently in fact). But, this time also noticed some video "sparkles" you would traditionally associate with an HDMI/cable issue. What surprised me was that doing a hard reboot on the ATV (no other devices restarted) seemed to resolve it. My expectation lately has been that the ATV will get a little sloppy in performance over a period of many sleep cycles, but I was surprised that it would degrade the HDMI in such a way until a hard reboot.