fullscreen windowed mode and second screen problem

[dantech]

When i play a game on full screen windowed mode like Destiny 2 and Assassin's Creed Odyssey and i play a video on YouTube or on Windows media player or any kind of video on the second screen the video lags like crazy. 

I have tried with AMD RX 570, AMD RX 580 and AMD RX 480 all versions with 8 gb ram 

I have tried with all the types of monitors i could get on my hands and all the combinations (DP,HDMI even with VGA cable with adapter to DP and HDMI)

My monitors are Samsung C27F591 connected both with DP and the other monitors i tried was  LG 24" with HDMI and LG 21" TV also with HDMI (this one was the test subject with the vga cable).

I did a windows 10 (1809 and 1803) clean install twice.

I have Radeon software version 18.12.1.1.

The rest of the computer is a Ryzen 5 2600 and a gigabyte ab350 gaming 3 and a thermaltake 850W psu.

 

I tried turning off the hardware acceleration on Firefox it didn't worked. 

On a more simple game like Diablo 3 i don't have that problem.

 

PLEASE HELP ME I'M NEAR ON BREAKING EVERYTHING !!!!!!!!!