In my DecaDynasty file, the traits of my IF-made-real have changed randomly. She was made real by my heir in childhood with the traits Clumsy, Shy and Eccentric. I then added Natural Cook at teen and Charismatic at YA. Now, she has Natural Cook, Charismatic, Eccentric, Daredevil and Party Animal.
She definitely hasn't bought a mid-life crisis, because I've been saving up her points to buy making-friends related rewards and a moodlet manager. She also hasn't used any premium content which might have changed her traits (the only premium content I've even used in this file is the baby swing, which isn't on the lot anymore and she'd never have used). I'm in Lunar Lakes. Her age/outfits/skills are unaffected, and both other sims in the house have their traits as normal.
It's not much of an issue as the traits she actually needs for career/skills aren't the ones that have changed, but I wondered if anyone knows what caused it? Mainly so I can avoid my heir doing it.