Usually Crabby stops short of Bulwark and kindly dies quickly. In this case, he jumped up and hovered while my guys killed all of the other baddies, and just kept hovering til the battle timed out, while my toons did nothing. None had charged enough to fire off a white skill.
This was on s6 in War.
Only thing i can figure is i had Satyr in my lineup, and the crab was trying to jump on her but couldn't land cuz of Bulwark?