Game engine has F12 button bound to make a screenshot and store them in own save location folder. In same time, Steam uses F12 button for screenshots by default too.

Each time the game takes shot, it freezes for a brief time for reasons. Steam doesn't freeze as it's overlay component works in separate thread, not interfering with games.

Open game console by pressing ~ button

Type in: unbind f12 screenshot

Close console.

Do note that bind and unbind behave different in new engine compared to older one and forks. Instead of overriding full set of commands assigned to buttons, these commands now add and remove actions.

Should not cause lags and break immersion anymore each time you make shots.