Bug preventing me from crouching

[Cant crouch]

I can't crouch in-game, which is rendering the game unplayable at a certain point where I have to duck under something to get any farther. I've tried both the "down" and "s" keys and nothing works. I've also tried mapping the key to something else. This is the only bug I've encountered. I have the most current game version.
Is anyone else experiencing this bug and how can it be fixed?