Had the same problem with Gulp getting stuck in the geometry in "Missing Scouts". I zoned out to reset the mobs, then went back in and killed the mobs that spawn Lureclaw and Gulp. Then I made a point of getting right up above Gulp before attacking him, just in the hope that having to come up to me would keep him from getting stuck in the floor.
I don't know if it made a difference, but it did work. Then Lureclaw chased us around some before we managed to kill him too.
Hope that helps.