Whoa, that gpu score...
In one of your earlier posts, you did mention a Corsair Hydro X custom loop. The gpu is part of said loop? Perhaps part of the waterblock isn't making proper contact.
I did have an issue with the GPU block when I first built the PC. Temps would instantly rise to 80'C degrees ,so I re-seated the block and added new thermal paste and it fixed the problem. Game I was playing then was Call Of Duty Modern Warfare (2018). And having done that haven't had any issues with it. But monster hunter is the only game I can't get even 60FPS on.
I should mention I was also having a problem with CSGO. FPS counter was showing I had 150FPS which is lower than what my 2080Ti should be giving. But the gameplay was noticeably stuttery, and performing really bad. But earlier I did a fresh install of windows with rufus, completely wiped my C drive, and uninstalled my GPU driver with DDU in safe mod. That fixed CSGO for me, now i'm at 200-300FPS and game is very smooth. So I'm kind of thinking with the new Monster Hunter ICEBORNE expansion. The devs might've not really optimized it. But some people are getting well over 100 frames.