Are they randomly generated per-game or per-session. Because I was playing for a bit and there was a blockage at the back between R3 and S3, but it was fine, since there was also a hole in R3-07 and S3-07 that I could crawl through, so I wouldn't interrupt my navigation when I was trying to find stuff from back there. But, then I left the game, because I needed a break, got back in, and when I tried to go back to that area, the hole was gone. If it was randomly-generated per-game, that hole shouldn't have just disappeared. But if it was per-session, as in leave and reopen the game, loading your earlier save, and it's a new session, that would make sense.