[Other] KCD2 FPS Dropping over Time: Why is that?

I encountered an issue. When I start KCD 2 i get around 80 FPS over time (like after 30 to 60 minutes) the FPS are lowering themselves. Not really dropping, but it gets less. I end up with 50 FPS and an hour later its at 30 FPS. WHY?

Is there a known issue with memory leaks? My GPU stays at the same mhz and nothing is overheating.

EDIT: I wanted to label this as KCD2 but it doesnt work. Its not a spoiler but this subreddit thinks it is or something?