One was just left of the cola bottle in the pit. "Left" might be a poor description, but I was fighting one of the creatures (either a 2-hit creature or a 4-hit creature) in between two blocks of stone, and rolling back rolled me through the wall to the right, slightly down, and (with enough jiggling) into the "hidden" cola bottle.
The other Time was in one of the abandoned indoor buildings, I think maybe the elevator building or the building with the oil? In the upper-left of the building I clipped through the ceiling, got stuck, and had to reload
The third time was in one of the cave sections where you exit a train car and can explore before going into the next traincar. I rolled backwards (maybe dodging an enemy) and through the wall, into the next cave section outside of a train car.
Sorry if that's too vague; if I catch the next build I'll pay more attention on my next playthrough.