After being stuck on this quest, I quit the game for a while (not because of this). Just went back in and now it isn’t an issue with being unable to kill all the monsters (stuck in walls), but it is stuck on the last objective of exploring all the passages below the broken grate. I spent about 20 minutes trying to hit a collision box, but no luck. This is at least the 6th time I have “completed” the quest, I guess it is time to move on.