Update: I was greeted by the ominous record block and protected content message. VSR was reactivated. Virtual super resolution renders a game at higher resolution for 4k game experience, but lowers the scale to your monitor's native resolution. Pretty stupid, if you ask me. Buying a 4k monitor and GPU would be better than trying to rig the GPU to perform a task it's not built to support. Somehow this is causing Relive to prevent recording. Everything is functional with VSR off.
Here is a screenshot of my settings, if anyone wants to copy them for testing on their setup.
↓↓↓↓VSR is turned off. ↓↓↓↓↓
If you can't get Relive to work with your game, try running in windowed mode before you start Relive. Relive doesn't allow recording with OpenGL games in fullscreen. You should be able to return the window to Fullscreen after the recording has begun.
I included my hardware for reference.
I was having this problem on my 5700 XT. Disabling/enabling DHCP didn't work. My VSR was off. I enabled VSR, screen flickered, and ReLive was able to record again. Disabled VSR, screen flickered and ReLive still works. Then I noticed my screen was 60Hz (it's a 144Hz). Put it back to 144Hz and ReLive still kept working.
It appears with the most recent update to adrenaline, Relive is now fully functional. Thank you AMD.