Scorpion and Worm fight - Recruit Marakketh story area

When killing the worm while its doing in and out burrow, it died while on top of the scorpion and caused the scorpion to get stuck and become invuln to everything but Kelari's brutality ability. Scorpion was doing no damage to party members but took far too long to kill with just one ability being able to hit. No debuffs or AOE worked either.