Expedition Bricked by Monster Spawning In Blocked Area

On one of the new Expedition maps (Sloughed Gully) monsters from the Runewords (Might have name wrong) can spawn in the areas enclosed by the root walls/doors and bricked the entire rest of the explosion chain as it will not move on until the monster has been killed. DoTs, Curses, AOE, Minions, nothing I've tried will make it through/touch the monster behind the wall.

Same thing, same map, same league mechanic, might even be the same spot.