I am experiencing the same thing. I was watching a show in Dolby Vision and stepped away for a bit. The tv restarted and the new software installed. Immediately after, I got the same unstable picture. I had to switch Apple TV to 4K HDR to finish watching the same show I had been watching in Dolby Vision a few minutes earlier. Very frustrating!
AppleTV 4K through a Sony STR DN 1080