Just droping this by cause I’m still playing. 
In last Apprehension level (the one where we fight Black Ops), right after I killed everyone, switched the lever to open the door, and quick saved the game, the fps dropped down very weirdly. I have quite descent PC, and had no problems through my gameplay with performance whatsoever (I don’t see the fps count but it runs very smoothly). Right after that quick save, frames dropped to - I don’t know, like - 5 to 10? When I turn around and face the ‘rest’ of the level (the side where the knockout sequence happen), everything runs normal again. But looking around at the whole chopper hangar causes mentioned problem.
I will see if this happens on my second playthrough. Just wanted you guys to know.