FXAA Antialiasing is dropping down

So I did not get any answer in technical issue section, so i try it here..

I have 2 monitors connected to my gtx1080 and now if I play on my second monitor a HD Movie or Stream the FXAA Antialiasing is dropping down on Crossfire Ingame.
FPS is still on 200 but the video isn't smoothly anymore..

In other games I didn't have this problem like in csgo.