Ideas
I was directed to this post from a post about never getting a high school graduation ceremony, however im not sure that thread should have been merged with this one because Ive never had the issue with the 3rd trait not appearing upon aging up. My issue is, in all the teens ive raised which is many bc i love family gameplay, i have only gotten the graduation event to happen once.
The 3rd trait not appearing is a side effect. The real issue is a stuck graduation event. If you had just 1 graduation event and then it never happened again, they probably assumed you had the same issue. I would submit your save file to EA_Cade as long as you don't use mods. If you use mods, you'll have to create a new save without mods and see if the same issue happens.