Game randomly caps at around 20fps

i have a very powerful pc. i get 120 fps usually with no drops. as the recent update dropped my frames have dropped to around 20fps. First the game would load and play intro cinematic all fine at 120fps but then as soon as it loads the in game menu the frames drastically fall. ive tried reinstalling , restarting my pc, updating drivers but nothing seems to fix the issue. Is this my pc or just the game bugging? id love some help