I have experienced this multiple times as well. Tried with a few different (vanilla) games and it was the same for all (sporadic, although it seems more present when there is a child with the angelic trait, but this also happened around YA and other adult sims). I did check the traits of all other sims around and none had the evil trait.
I also have a mom sim who occasionally gets the "sad about evilness" trait from her toddler. There are three toddlers in the house, so I'm not sure if it's all of them, or just one. I do have one "fussy" toddler, so I don't know if that's a trait that can set off a "good" sim.
I have only run into this with Angelic toddlers. One of the sims who received this moodlet had previously raised a Clingy toddler without issue.
Since the last patch I've also had this problem. My Sims with the Good trait are getting the sad from interacting with evil sim moodlet from interactions with toddlers. Never had this problem before so I think it's got to be the recent patches.
This happens on PS4. My Good sim will have both good moodlet and sad about evil at the same time. He'll get sad about an evil sim when he's just sitting there doing homework not interacting with another sim at all.
Here he had been chatting with his brother, who does not have an evil trait.
Here he had just finished homework, alone, and then went to get food.
My adult sims are: Dad (Father Winter) Childish, Good, Cheerful, and Gregarious / Mom Family-Oriented, Good, Neat, and Business Savvy
Just like everyone else, this doesn't happen all the time, but the dad doesn't leave the house and only gets this after interacting directly with the toddler. Most recently, reading him a bedtime story got the "sad about evilness" moodlet.
Never used custom content or mods. Have all packs. I only noticed it in the last few weeks (It's currently 5-03-2020), but I don't remember the last time I played a good sim.
Uploaded to the gallery as "Father Winter's Family" with #SadAboutEvilness to help with search. Dad still has this moodlet if those are present on download.
I'm getting this issue too. Current household has 2 YA vampire sims who both have the "Good" trait, and their twin toddlers both have the "Angelic" trait. I've noticed the "Sad about Evilness" moodlet seems to pop up when either parent interacts with the toddlers, but I noticed the mom had the moodlet when she hadn't interacted with either toddler recently enough to trigger it. Is it from being in proximity to vampire sims, even though 2 of them are toddlers and none of them have the "Evil" trait???
For the record: I do not play with mods; I do have some CC, but I wouldn't think that those items would trigger those moodlets, especially since I've had this happen with other sims in other households where there is no CC, and even with sims that don't have the "Good" trait.