By going too fast (with a handmaiden for example), some scripted spawns are skipped, and we find ourselves unable to complete the objective because map is empty of all ennemies.
It seems that enemies killed indirectly (by pushing into river for example) does not count towards the goal. But it should probably be checked as well.
Did said HM pull and die far from team? That causes enemy to despawn in all weaves. Major issue if it’s not one of the more “generous” maps essence wise.