FPS drops constantly.. any idea of what could do it?

[Jone.1632]

So when i'm playing it works fine... 30% of time its like 75 fps with everything maxed 1440p... And then suddenly it goes to 5-12 fps and when i look to Task Manager Guild Wars uses
2.0 - 4.2% Cpu and 5.0 - 6.3% GPU. When it normally works it takes like 34% Cpu and 45% Gpu... So any idea what could do this?

My Specs are: i7-8700k, 64gb ddr4 and gtx 1080 ti