I have a child (born and raised in-game, not from the gallery) just aged up from toddler a sim day ago, and she has a moodlet for the Grouch trait. Never had it. I picked Genius when she aged up, and that's the only trait she's ever had. I haven't even gone to CAS with her as a child.
It's an old save brought back to life when I wanted to rebirth a favourite sim from ages ago. Maybe that's relevant. The bug is on a sim born recently, however.
https://drive.google.com/file/d/10omXsiJzgMFf5Xeyg9ICtPcbpfOGd6Hw/view?usp=drive_link
A Sim who does not have the Grouch trait gets a negative moodlet about Sims being kind to him.
No Sim in the household has the Grouch trait. During Kava party Sims were doing friendly interactions. My played Sim got a moodlet of being very sick and disgusted (uncomfortable +40) by other Sims' kindness from having a grouch trait. His traits are cheerful, nosy, lovebug, family oriented and domestic. This Sim was created in CAS as a young adult. Domestic is a reward trait. Nosy is a discovered trait.
Platform: PC
Gamer version: Newest
Bug occurred: After Jan 14 update
Mods: None in this save
