I figured out why my child sim picked up some skills, but not others- no saving, AND also no loading screens! Just like with the Acting bug. I had to travel to try fishing, no fishing spots in my neighborhood, and then didn't try video gaming until she went home again. And with Charisma, she maxed Social while hanging out in the park, and then almost immediately got Mischief on her own. And then she went home before trying to pick up Charisma.
I originally didn't care much about Fishing, but then I decided I wanted the family to go camping, overlapping the end of summer/beginning of fall. Fishing is one of the major things to do, especially for a kid who can't collect the plants, so it would be a real bummer if she can't raise the skill. So, I reverted her Mental to 9, maxed again, went to the park and tried fishing. Still couldn't get it. Wait, what if loading screens do it too? Reverted her Mental again still at the park, played chess till she maxed again, tried fishing... Bingo! Then I had her play a game on her phone and she got Video Gaming too, before going home.