Looking at you Sanctuary Onslaught, Survival and 'Kill x enemies of a certain type' (especially drones) bounty stage.
Either up the spawn rates or lower the amounts you need to kill.
This is even more prominent when playing solo.
That (4-man) Interception for the proxy rebellion that still bug out and only spawn 4-5 mobs at the same time.
/u/rebulast maybe a fix for the next time?
Ah yeah, next time.