CS2 performance goes down by 50% when playing for hours, why and how to change that?

I've seen many many times that the performance on my PC drops by 50% when playing for hours in CS, and I've also noticed that restarting the game solves the issue, I have a RX 6650 XT, a Ryzen 5 5600, 32GB RAM 3600mhz, 1tb SSD, I have no overheating issues as far as I know (I have a 240mm watercooler for the ryzen and the 6650 XT has 3 fans on it) normally I play at 260 when starting the game, but after 1 or 2 hours of gameplay i can get down to even 80 fps on some heavier maps, and after restarting the game it goes back to 240-280 fps, help??