I decided to challenge myself by starting a warrior on Nightmare. I've made it to dungeon level 13, but of all the quests Ive done, only one has given the expected loot (the empyrean band).

Other quests that should have dropped specific unique items (Griswold's edge, for instance) only gave randomized loot (in the same category, it gave a sword, The skeleton King gave me a random helm etc)

Is this intended? It's been a really long time since I played on higher difficulties, but I don't think this was the case before.

Edit: To be clear, I am playing single player. Using Devilution X version 1.5.4

Single player mode originally didn't have a proper difficulty mode setting.
Not sure if that's the intended behaviour or not for DevilutionX to give a different item for quests in higher difficulty levels… but I suppose that might be what they mean by this: in the changelog of version 1.5.0

Edit : according to https://github.com/diasurgical/DevilutionX/issues/7124 it seems that is indeed the intended behaviour.

Guess that answers that. Thank you

Constance is right, the intent is to drop more usable items on multiple playing through. The items aren't completely random the quest will still give an item of the same type.