Question Suddenly - Second monitor causes problems (low fps, stuttering)

Aug 7, 2019
Hello good people!

I will just go straight to the point:

So I've got two monitors (144hz Predator and 60hz widescreen LG).
They are connected to my GPU through Displayport (144hz) and HDMI.

Everything worked fine. I was able to run a game on my 144hz monitor and on the second one I was able to see something else like facebook, tutorials, discord etc.

I'm running games on SSD (if that matters).

Yesterday when I tried to play ANY game, the second monitor went black and the game had 5-15fps.
When I alt-tab game it goes back to normal, I mean it is happening only when I click on the game.
(When I alt-tab the second monitor goes back to normal and I can see that my game is running with 144fps or more. When I click on the game - BOOM - it goes back to 15fps again...)

I tried fullscreen, borderless and window resolution but only game in window works (no lags or whatsoever).

The ONLY solution for now is to unplug the HDMI cable. After unpluging HDMI everything is working very well on fullscreen etc.

What I tried:
What I didn't tried:
Also: Temperatures are OK, I mean when I play any game I've got like 70-80 degrees on GPU and 70~ on CPU

My PC:
Windows 10 Pro 64x
CPU i9-9900k
GPU Aorus Geforce GTX 1080 Ti Xtreme Edition
PSU Corsair VS650
Motherboard Asus ROG Strix Z390-H Gaming
RAM Aorus DDR4 16GB 3200Mhz
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