In my first play-through, after completing the columnar building with 'diving boards' that face each other across the center, I triggered the exit door. It appeared to open but I couldn't get through, not on floor, walls, nor ceiling. In sum, it was functionally closed though visually open. I saved and returned to that point, at which time I had no difficulty walking through the open door to the platform where the 'God Cube' will appear.
I'm using Win7Pro on a very capable gaming computer I built myself a few years ago; it doesn't glitch much. I downloaded the game from Epic.