JKLS Event: Threepio and Chewie

I can't tell exactly what's wrong, but during tier 6 of Jedi Knight Luke's event, Threepio and Chewie sometimes just don't do the extra instances of damage on their AoE. It might have something to do with the stormtroopers, as I noticed they seemed not to take a second instance of damage after I killed the officer in the first encounter.