UPDATE
Thank you to user /u/ralcar for informing me that this is getting fixed! It’s in the next preview of Windows 10 2004 20H1! So yay guys seems I’m late to the party but we’ve got a fix on the way!
Disclaimer
Just from the get go this is an issue that seems to affect G-Sync monitors. I am not able to test with freesync but I’ve had this problem affecting me for years and never known it was to do with this till I actually got off my ass and figured it out. If this this widely known! Sorry! Hopefully I’ve helped someone!
Backstory
I have a G-Sync monitor. Whenever something drops to low FPS whether it’s a level loading or the game just gets choppy, performance in other applications are hampered even if they shouldn’t be. World of Warcraft is one of those. It’s always running and when I tab out I have it drop down to 30FPS. This causes applications weirdly on my second monitor to match this frame rate. To test this issue I dropped it down to 8FPS and it got even worse. The biggest issue of all, is that whenever I hearthstone the game loads and drops down to 1FPS causing everything to become unusable on the second display.
The Fix!
Now the simple fix would be to just turn off G-Sync. That’ll stop whatever this issue is. We’re going to look into why this is happening, but a quick workaround is just to open something graphically intensive on your other monitor. In my case, I wanted to record the problem happening, but opening OBS fixes it. Interested to learning why this is happening and if anyone out there has any deeper insight into why, would love for you to share in the comments below. I’ll update the post as we learn more.
Things Tried
I did my research! I tried thing such as editing Nvidia Inspector settings for multi monitor optimizations along with a barrage of Nvidia Control Panel settings of GPU Scaling etc. Nothing seemed to work except turning off G-Sync or having another application open in this case OBS to stop it happening.