Stuttering picture

I have 100Hz monitor, the game runs 100FPS (Ctrl+R shows 100FPS) but it looks like 40FPS, I thoght that it’s just old laggy game engine untill one day magicaly game picture transformes to pure 100FPS, next location and it’s again like 40 FPS… Well, if you hit ESC button 5-50 times in any location, the game starts to run perfectly, next location and it runs laggy again untill you hit ESC button 5-50 times again. Fix it pls. Any other games run perfectly. i512600K, 32GB RAM, 2060S, 750Watt Power supply, win11, latest drivers.