mobs bugged in HS dropping through floor

[Hisamori]

Twice I have had mobs in north wing suddenly drop through the middle of the floor. I thought it might have gated but these were SK mobs. The first time it warped and I believe it went to East because when I zoned back in after gating, a huge train was going back from North to East from through the entrance. There was no one else in the zone so it couldn't have been someone else's train. The train also took a long time to get to me.

The second time, I saw the mob come back from an area other than its spawn point.

This is really weird behavior and makes the zone almost unplayable given the long CR process if you die here.