mikakala A double load (load the household or lot, get an error, reload that same household/lot without leaving Manage Worlds) is a known troubleshooting step for this kind of problem. It clears out some mod-related data that could be generating the error in the first place. So you could try doing the same thing again to see whether the save plays normally.
There have been some issues reported with sims aging up too early, but the most recent problem I've seen that wasn't entirely mod-related was fixed in patch 1.110:
https://answers.ea.com/t5/Bug-Reports/FIXED-Sims-age-up-go-back-in-age-days-added-reduced/td-p/11693048
If this keeps happening to your sims, and a death might be an early age-up for an elder, I'd suggest disabling aging for at least a sim-day, and saving that way (use "save as" to create a new save rather than overwriting your current one), then quitting and reloading before reenabling aging. And do check the sims' personal info to see whether their current ages have changed.