Sims not doing actions

I have a teenage sim building a school project and he's got to level 3 art so far but the project box is still unopened in front of him and he's just sitting there staring at it.

His twin brother is making apple jam and he's got to level 3 cooking but the ingredients on the chopping board are untouched and he's just standing there staring at them.

Their mother is fishing, and she's catching fish, and their other teen brother is playing violin with emotion and I think he's acting normally, but these two are not. They're not completely frozen in that they are sort of swaying in place, but that project box isn't going to get him performance at school just sitting there unopened!

It looks like the same bug that sometimes when you tell a child sim to make a drawing at the craft table, they just sit there at the table gaining creative skill but not actually progressing their drawing at all. I can't find that bug report now but I've seen that happen in my games a few times now. I know that the immediate fix is to leave the lot and come back, but that's really annoying when it means that every sim who was doing what they were meant to be doing - including the sleeping infant - will be somewhere else doing something else when I get back.

I would like this bug to not happen, please. When I tell a sim to do something, I expect them to do that thing.

Never modded or cc, on PC, lots of dlc but not the most recent stuff.