@Faerin and
@Playalot Sorry to take so long to respond, but I've been watching how the UI portraits line up in my game to see if I reach any conclusions.
In short, I occasionally notice that my sims portraits change their order, especially after a birthday, but then the order seems to correct itself the next time I load the game.
Honestly, when compared to some of the really bothersome game glitches I've experienced (conspicuous lagging, broken aspiration counters, crashing, long loading times, lost retail perks and collections, culling), I don't bat an eyelash at household sims lined up in the wrong chronological sequence.
I guess it's all relative.
I don't mean to trivialize your problem
@Faerin My short answer is: the portrait sequence eventually corrects itself without my doing anything about it.