OK. Thanks all for the info.
Hi Crin! Adding a "me too" on this.
Sims are completely forgetting they ever met anyone who wasn't at least friend level or a relative. All the forgetting happens while I'm playing another households. I haven't tracked it yet to see if there's a particular time of the week that it's happening - tonight is the first time I noticed the forgetting part.
I've also had Sims develop sudden full-on friendships while I'm rotated away, even if I've not seen those Sims be together - or be at all - in the surroundings when I'm playing another household. And I had one sudden enmity with that too, between Sims who hadn't met or been seen at all while I was playing other Sims. I'm not sure if it's related or not, but it adds to the frustration with what's happening with acquaintances.
Thanks Luth
Just to add to what I found:
The relationships disappear any night. If I rotate to the household of an acquaintance for a Sim day then rotate back, that will be the only remembered acquaintance. This makes the game pretty near unplayable for rotational play.
