No last names?

My mom and I both play the sims using the same origin account, but she doesn't post on the forums so I'm posting this issue for her. Recently (a week or two ago, about) she's noticed that many of the sims being born into her game don't have last names. I thought that at first it was just because her sims were having kids with sims that don't have last names, because I had a family of sims that didn't have last names who were the children of Bertrand, the ghost from Windenburg. But at this point, unless some sim without a last name is really getting around, and this is happening across multiple saves, that seems like...yeah, not it.

She and I both play modded but she says that none of her mods make sense with the problem. Is anyone else having this issue or have an idea about what mod is causing it?

Thanks for reading. :)