Crucible Challenge Stage 3 Bug

When the Karnifs/Wind Spirits first spawn, I would destroy the barrel to distract the mobs. I am able to AoE combo them all to kill them in unison, however, in doing so this causes the next mob to not spawn, forcing me to leave the dungeon and wasting a run. I have tested killing the mobs one by one, and then it spawns the next mob, but not when killed all together at once.