I've gone through the first bit of the puzzle, into the circular room with the 4 numbered platforms kill the mob, grab the scorch cannon and shoot the thing next to the door. The door rolls up but there's a barrier behind it and the door slides down again so I can't get out. If I shoot all the scorch cannon ammo, the mob that carries it respawns, I kill it again, grab the scorch cannon and it's the same story. Door opens, then just closes again and I can't get through. All the puzzles in the room have been solved so how am I stuck? Could it be some mob fell off a platform and hasn't counted as killed?