Yes they all died happily old age!
Yes, i have a saved back-up. I just tested it and, unfortunately, the same issue is still there. My ghost sims who died of old age are now alive. Even on my back-up save
I can second that. I have a save with many playable ghosts, varied causes of death, including old age. All those ghosts are okay.
In my newest save I had a playable ghost whom I downloaded from the gallery. He is an adult and just now he appeared as a passerby in a park, alive again. I did a save_as and loaded the previous save again, this time checking on the household the ghost is in. He showed up as a ghost in household managemant and still was aghost when I opened CAS (cause of death: Old age), but when I loaded the household, he spawned as a living/non-occult sim. So in my case at least it was a mismatch of age group and cause of death.
You are correct. My Sims died of old age, and then I used MCCC to age their ghosts down to Adult (because I didn't like they way they looked and acted as elderly ghosts). When the update came out last week, that confused everything. But I got it sorted now. Thanks again!
