Game Mechanics: SolB mobs appear to be falling through zone

[uygi]

Mobs in SolB appear to be falling through the zone randomly. Had a FG this morning fall through and tank had to sit to get him to come back. Skarlon was on track and trackers were zeroing him in on his normal spawn spot, but he wasn't there. He was visible on client trying to run out through the LS zone, but he looked like a cyclops there, and he could not be cast on and pets would not aggro him.