GPU Usage degrading in time

Hello everybody!

When I boot up the game I have +240fps in my hideout. The more I play the game, it gets worse and worse. After 2 hours of gameplay, the same hideout goes to 108 fps MAX. I was checking my GPU/CPU usage/temps and I must admit my GPU was surprisingly low ( 25-50% at max during heavy juiced maps ).

CPU : I9 12900K
GPU : RTX 4080 SUPER
RAM : CORSAIR VENGEANCE DDR 5 5200 MHZ
PSU : CORSAIR 750W
MOBO: ASUS PRIME Z690-P

INGAME: Build: Ice Nova of Frostbolts with cosmic MTX. Power charges spheres mtx New league weapon enchant (the blue one, can't remember the name)

What I've tried so far:
Changing some settings in the Nvidia control panel
Uncap my FPS
Cap my FPS
Delete the game and the shader folder and reinstall the game on SSD
Remove sound Q's
Reinstall Nvidia Geforce Drivers
Checked if my GPU is seating properly on the right lane
Disabling ALL MTX
Check CPU/GPU temps (all fine here)

This is how it looks when I boot up my PC and after 1-2 hours of gameplay mid-fight



And this is how the game is doing AFTER 4-5 hours of gaming


My HWINFO


I was thinking maybe there's an issue with the MTX i have? I was wondering if anybody else has these issues. I'm pretty sure my pc should be able to handle the game at ~160-190 fps while mapping. Also need to mention I'm running 240hz 1080p monitor. Also, everything under settings is set to LOW.

Hope anyone can help out as this drives me crazy! Thank you very much people!