In my experience it seems that it is caused by repeatedly coming in and trading with them, mistral seems to think trading is the most hostile action ever, worse than torturing people slowly with a spoon, just do not trade with them or periodically clear their "memories" by bringing them together in a room with non trading npcs and having them all talk together until they forgot the context where they were insanely rude and did nothing but spout insults, they clear context when it is too full.
I think the prompts that trading generates should probably be changed, right now, it seems incredibly rude to the AI and only majorly sociability favoring personality traits can help counterbalance the issue.
Aldric is marked as "professional" in his personality prompt, if professional means making conspiracy theories about turnips, insulting people based on their clothing and telling people they should not be buying stuff from them while dismissing them under the pretext they have work to do, I have no clue how he ever gained any money.
Wait, you managed to get Darian to not be nice with you? How did you do it?
I suspect it is the post interaction "tell other npcs about interaction" system, all the merchants being really angry at you for daring to buy things from them probably added to the context of Darian stuff like "this man is dangerous, evil and the harbinger of the end of the universe, he dared buy something from me, you are a guard, you ought to keep watch on him and try to put him in jail for his insanely evil crime of paying for stuff."