I've noticed that on some occasions during a Harrowstorm, the Gray Host champions (the Vampire Lord and giant Werewolf) aren't being summoned in any of the stages, so you just have to deal with trash mobs. This makes the Harrowstorm a lot more on the easy side, and imho, not as fun
I'm not sure if this is a bug, or deliberate. From what I understand, if enough lost souls touch the spires, the champions can be summoned. When I arrived on scene, there was just a level 8 who kept dying over and over, so I assume the champions should have been summoned already, but they weren't there, nor were they there for the rest of the Harrowstorm.
It'd be great if they could always show up, because they make it a lot more interesting than it already is.