It was a part where there's the real big drop, just after you discover the circles that open up into squares, I believe? I was going through a portal that made everything black, and then I had to navigate through invisible walls, which made it impossible to progress :(
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Ah yes, in fact that might be kinda intentional! The walls are supposed to be "invisible" yet the camera should've zoomed out to show some platforms below the floor. Those platforms should show where the invisible walls are as if it was a reflection. I guess I could make it clearer in a later build.