I did some testing, and it seemed to happen when the sim died on the same lot as me.
it happens with plenty of sims i get phone calls about who are not on my lot (which coupled with the phone calls not actually giving you information bug makes it very hard to tell who has died ever lol), I think it's random tbh
I've had this happen with sims who I created as ghosts in CAS, so not just dying on the same lot. In this instance it was sims who didn't die of old age. But who knows if that's just a correlation rather than a cause of the bug.
I created my sim's family as ghosts in CAS. The 2x ghost sims who didn't die from old age (death by pufferfish & overheating) showed as alive in the family tree.
The Sims Team
