Personally, there are only three enemy types that annoy the hell out of me in Darktide:

1) Shotgunners with their infinite stagger resistance, absurd damage and unwillingness to engage in melee.

2) Hounds because they are complete and utter jank. I think my dodge rate against them is like 3%, while even well timed pushes seem to only land 70% of the time. Add to that seemingly random stagger resistance and you end up with the most frustrating special that has killed me more than any other unit in the game.

3) Hordes upon hordes of lowly shooters. Damnation loves to spam these bastards everywhere, and they deal far too much damage compared to their melee counterparts. The armored dreg/scab footsoldiers are a complete and utter joke when compared to even the most basic shooters, and I don't think that should be the case at all.