My sims suddenly despise each other?

Sims 4 on PC: Have found recently that my sims' relationships (household and neighbours) keep rapidly going from almost friends to strong dislike and/or despising each other. I have not made them do any mean actions towards each other; they have only interacted once or twice and got along well. I have Neighbourhood Stories disabled and there are no negative sentiments attached, so can't understand how their relationships could have deteriorated so quickly.

One of the sims involved has the Uncontrollable Hissing vampire weakness but this doesn't usually deteriorate relationships that much. He and his neighbour have now gone from acquaintances to despising each other without even interacting since their last meeting! Not sure if this is a bug or the game's background relationship AI going over the top.

Does anyone know where I can find a salmon so I can make Potions of Forced Friendship and fix this?

I have Island Living, Eco Lifestyle, City Living, Werewolves, Realm of Magic, Vampires, Spa Day, Paranormal Stuff, Fitness Stuff, Spooky Stuff and Moschino Stuff installed.