I have no idea why, but all of a sudden my game started crashing whenever i touch a turret, pick up a turret or a turret activates. This doesn't happen on the regular game, only on the source unpack. It worked just fine until now but all of a sudden it just started crashing. Any help?

try reinstalling

Did you recently change something in the settings? I remember having my game crash in specific situations when the "portal render depth" was too high.

I managed to fix it by resetting unlocked chapters, i have no idea if this is the ultimate fix but atleast it worked