OK. I finally found the fix without going to Nvidia Control Panel. The problem seems to be related to the fps in the game. The game was originally intended to be played at 62 fps (with the bSmoothFrameRate option as true). Now we're going to use that option but we're going to change the maximum fps from 62 into whatever we want (165 fps because I have a 165 Hz monitor in my case).
Set:

• bSmoothFrameRate=True
  
• MaxsmoothedFrameRate=165.000000
  
• MinsmoothedFrameRate=130.000000

Documents\My Games\KillingFloor2\KFGame\Config\KFGame.ini


When in game, make sure you have the option Variable Frame Rate Off like this: