[NEEDS SAVES] Sims forget already existing relationships

I'll do that, thank you very much!! 

This has started to happen in my game as well, after the resent game update. I have all packs except Eco Living, and I have no cc or mods. My sim is in the doctor career and got to know a sim from one of my other households at work. They built quite a good relationship, the friendship bar was about halfway full.Today when I turned my game back on, I wanted my sim to invite the coworker over, but discovered that they don't know eachother anymore. Like the OP, I have also been playing rotationally with these households.

Since June update (I have no Eco Living) NPC Sims forget my Sim. This happens with different Sims in different neighbourhoods.

E.G.: Every sunday at the starlight-event my Sims have to re-introduce themselves to Sims like Thornton Baily a.o.

Every Sim-Day, when my Sim returns to the realm of Magic, he/she has to introduce again to the "Spellcaster-Teachers" (Morgyn Ember, L.Faba etc.) and has to rebuild the relationship, so that they teach him/her. Every Sim-Day the teachers forget my Sim, even if the relationship was "friends" one day ago.

This only happens since the update in June.

No Mods, no cc, no Eco.

I also just recently developed this problem since the most recent patches (June, July). I started a sim in July who lives in San Myshuno and went to university, so she meets new sims regularly. But she keeps forgetting them rather quickly, even the ones she lived in the dorm with (so, talked to every day). I tried to create a Get Together club for the teammates she played e-sports with at college, but she didn't remember some of them anymore so now I wouldn't know how to reintroduce her to them. She makes friends with neighbors in San Myshuno and days later forgets them. I saw some comments mention culling but I've pretty much only played this household for the past couple (real-life) weeks and she forgets people within a few Sim days. Why would the game be culling Sims that quickly?  It's not like she's forgotten an NPC she met weeks ago in real life time. She meets a sim on a Monday in the game and then forgets them by Wednesday when she runs into them again at the food stall.

I do have mods but I'd be happy to backup my save files and test without if that would help. But it looks like others without mods are having the exact same problem.