TLDR; My resolution was to perform a "Reset and Update" AppleTV.
I have this issue too and was trying to respond to Thread #253806083. Basically AppleTV and TV (in my case LG C9) keeps trying to "renegotiate" Dolby Vision whenever content changes.
My setup is LG C9 + Sonos Arc + AppleTV. My cables are all "specced for 4k 120Hz" and are well shielded products.
It became extremely frustrating with Youtube especially because ad content would knock the TV out of Dolby then regular content would bring back Dolby. So two black-out events per ad. With multiple ads, the TV would just hang out in No-Signal-Land until we're well into ~6-10s of steady content.
This happened for Youtube, HBO Max, even TV+.
I've power cycled my entire entertainment center and factory reset everthing, one by one. Testing in between. The last thing I did was reset AppleTV and the issue resolved.
Hope that helps.