Youtube on second monitor stutters while I am in the game

First of all, it is new problem both on Vulcan and on DirectX11. I have never before encounter this problem. Nor playing PoE or other games.
I have two monitors:
One is 100Hz refresh rate - GSync connected via DisplayPort to my GTX 1080
Second one is 60Hz standard monitor connected via DVI to the same card as above.
Usually when I am playing I am watching in the same time on second monitor Youtube, TwitchTV, Netflix - you name it. It was always fluent without any stuttering or crashes - nothing.
Now, when I start youtube or other movie services, doesnt matter whether full screen or in the window (on second monitor) - when I am entering game after I choose my character - it start stuttering on second monitor.
That's interesting that when I am on character selection screen it still fine. As soon I am "in" the game, problem starts.
I tried:
- change to DirectX11 - it is a bit better but still stutters.
- change connection of second monitor via HDMI to onboard graphic card (IntelHD) - no change
- enable and disable hardware acceleration in Firefox (thats my main browser) - no change
- change my browser to new Edge based on chromium - it seems that there less stuttering but it is still there.
I have no idea whats wrong, of course all other games including very demanding like The Division 2 cause no problem at all.

Problem solved by reverting back to 442.59 WHQL Nvidia drivers.
Thank you Guz!