I started experiencing this bug recently, so I'm afraid this is still occuring with (some) Simmers. I do not play with mods due to fear the game will even be more buggy :(
What I'm experiencing:
I play one main household in a legacy challenge. The mother of a household member died. Then she died again. And again, every single Sim day! She wasn't greyed out in the fam tree or relationship panel. Went over to the household the mother had lived in: 8 members in the household, mother was not one of them! So wtf right? When I loaded into the household, there were multiple urns but not the mom's... But she was gone from all relationship panels in the household, and she was greyed out in the fam tree now, even when I went back to the main fam. I could live with this outcome.
Fast forward a couple of human days and at least one Sim week. The main household bred some horses. They wouldn't age up from filly to adult horse without changing the auto age up settings (a fix I found on reddit). Ok, could live with this. Then I split the main household and let the horses live with the branch I was going to leave on another lot. Set them up with all horse necessities and stuff. The horses were old so after some Sim days the main household was informed of their deaths. AND THEN THEY KEPT DYING. EVERY SIM DAY. They didn't grey out in the relationship panel, just like with the mom situation above. Went into the household I left them in. They were gone there, but still present (not greyed) in the relationship panel. No graves. And the Sims in that fam were also grieving these horses, again. I now realize I should've tried to see where the horses were at if not with this household and still 'existing' in the game, but it shouldn't have been possible for the horses to be removed in the first place: the household was set as an active household so neighborhood stories couldn't mess with my planned story.
Eventual fix that seems to be helping so far:
I added the horses back into the family. I had to invite them over from the relationship panel (lol) and add them back to that family as soon as they appeared. Then I went into cas.fulleditmode and deleted them altogether. I haven't received any 'horse has died' calls yet.
The Servo in the household can't drink the effin' moodlet solver so she'll have suffered through almost one Sim week of constant mourning for horses, during first week of uni I might add, while I tried to fix this issue.
I hope this helps!
The Sims Team
