hi, only a suggestion but trying display port instead of hdmi may help. Although this sounds like a problem of waking from the sleep state, I imagine it doesn’t happen from a cold boot.
one other consideration is if you have upgraded the graphics drivers but without a complete uninstall and then reinstall I believe this may lead to problems. I have a Radeon 570 and used to upgrade with each new driver and I did see problems a bit like this. I eventually did a removal of AMD drivers and a complete driver install. Since then no problems. It does mean I am still on the version 19 of the drivers though!
i hope this might help, it is probably not a hardware problem.