When growing up, I gave my Sim the the extra trait he was entitled to but now it’s missing.
- Manually add the trait
- If the trait still does not stick, take your sim to the mirror and change his hair and then add the trait again. Also make sure to change the tabs a few times to see if it really didn’t stick.
How to prevent (theory)
On the window where you choose the trait there is a little picture of your Sim. Wait until it has completely changed to the new age group before pressing ok.
Not this issue
If you are missing ALL your traits (especially in CAS) that is because of incompatible mods in your game. Remove the mod and clear your cache files. If you saved your game like this you will need to add the traits back manually as well.