I recently got an LG HDR compatible monitor. I run with HDR on and for the most part have no issues.
I have played 2 games since I got the monitor - Nier : Automata works fine, I also play an older game called Outland. Playing Outland is fine until I exit the game - the game seems to flip out of HDR and then re-enable it when I close out. The issue is that when the HDR is re-enabled the white point is not set correctly. White seems to be slightly pink/grey and the image has a slightly washed out look.
I am also seeing the same thing occasionally when I go fullscreen with a YouTube video. Randomly the display seems to lose connection and I will see a black screen with random blocks of colour and again the image being washed out when it sorts itself out.
Solving it is easy, I just go to Display Settings and switch off/on the HDR setting and then all is back to normal but that gets annoying quick.