I reproduced this issue in a new save with a new family, and I have for you the save from right before and right after the kid ages up. This zip file contains a before folder with the before save, an after folder with the after save, and a folder with some screenshots.
https://drive.google.com/file/d/1HgQj6rttFSIaYm7OKk9GpgUtqHURp6Ta/view?usp=share_link
The way I reproduced this issue is:
Create a kid, create his mother and his father using genetics, make the father a ghost, create an unrelated household member to be his mother's new spouse, set the spouses as married. When I loaded the family into a house I immediately set the tombstone for the father in the garden and had him go into the light so his ghosty self would not be a factor in their lives from then on. The step-parent immediately adopted him as a care dependent. Then, the living parent and step-parent raised the heck out of him, instilling all the character values they could. When he aged up, he got 4 positive traits. His bio mom got the achievement in the super parent aspiration and his step mom did not.
I am hopeful that providing the before save will allow you to do some sort of trace while the age-up happens and see where the process goes wrong.
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