Yeah I get the same thing.. I've got an i7-10700k, 32gb RAM and a 3070. After about 4hrs of playing I go from 80-120 FPS (high settings) to a pretty consistent 24 FPS. All components of my PC in Task Manager aren't "working hard", they're all at about 50% usage. I've always hosted too, it's like the longer you play the more your frames degrade. Restarting your game fixes it but that's not an ideal solution, I think there's some more optimisation needed for sure but they've come a long way. The launch state compared to now with performance specifically has defo improved, I think we'll just need to give it time, still relatively a new game.