Ideas
Attesting that this is still an issue that I recently came across yesterday evening. I'd been playing with my Butler having recently purchased the Vintage Glamour stuff pack from one of the many end of year sales. My Sim's family welcomed another set of twins since, who have aged up entirely to adulthood through thorough gameplay. Having recently welcomed my Sim's latest child and aging up to toddler on their simulation birthday, after I returned from CAS Juelz was no longer my sim family's Butler and some rando named Angelo magically appeared on the lot with the Butler title.
I've had this happen with Ranch Hands too. Ranch Hands are the WORSTTT in the game. They hardly care for live stock, always dumps trash and welcomes themselves into my sim's home though they aren't welcome by me 👿. That and they never leave at 7PM when they are meant to.
The largest frustration is knowing what work I put into any NPC sim has the probability of glitching which can ultimately undo the tedious work I've done in cas.