Invisible Collider...?

Hi! I'm new to Unity 3D and have been following the Survival Horror Jimmy Vegas' tutorial, but found this problem. I'm using the standard Unity FPSController.

It seems like an invisible collider, but there's nothing there. The floors and walls are aligned. The point where this happens isn't a division between the floors...

I looked up everywhere, couldn't find a solution. I made a video so you could understand it better. It's kinda hard to explain, really.

 

Check all your objects' colliders, they might've got messed up somehow after scaling, etc.