It's hard to describe and I don't really want to take a video of it because of where the issue occurs. Basically, if I have a chrome browser tab open on this monitor and I started switching between emails or tabbed categories in Gmail, my WHOLE screen brightens up then goes back to normal. This happens pretty quickly. If I move that same tab over to my secondary screen which is an IPS display (also LG), it doesn't happen. Move it back and each time I click between emails or tabbed categories my screen drastically brightens then goes back to normal brightness. It's almost like the entire screen goes white for several frames then returns to displaying normally.
I'm not sure what's causing it, and as far as I can tell it only happens when I'm in gmail. HDR is on in windows and on both displays. If I turn off HDR (Win+Alt+B), it still happens. I believe I'm on the latest firmware for the monitor - updated it less than a month ago via the LG software. Happened before and after the firmware upgrade.
Primary monitor (27GX700A-B) is at 2560x1440 @ 280Hz, other monitor is same resolution but 144Hz connected to a 5070 Ti with g-sync full screen mode turned on for each.