When one of my sims was at university, the lecture in the Student Union building was a disaster. Everyone tried to leave at once; meanwhile, all the students for the next class were trying to get in, so the door was completely blocked for hours. Four sims peed on the floor, all of them claimed to be starving ... it was ugly.
So I went into Edit Town mode, did the "EnableLotLocking" command to gain the ability to edit the Student Union building, and added another door to that room.
When I sent another sim to university, she kept not being able to go to class. I tried removing mods, clearing caches, all that stuff, but she couldn't go to class.
Then I noticed that she would get the pop-up notice that says that there's a meet and greet at the Student Center, but the command to go there dropped from her queue, and when I sent her to the Student Center manually, the usual "meet and greet" stuff wasn't in the building.
Replacing my edited Student Union building with the original version made it all go smoothly, and now my sim can go to class.
I added one lousy door! It looks like the script that runs the "meet and greet" event expects the Student Union building to be a certain way, and ANY deviation from that causes the script to abort. And aborting that script means that your sim's student status isn't initialized properly.
So, for anybody else who -- like me -- enjoys tinkering with things, don't mess with the Student Union building!
Sheesh. One lousy door. *shakes head*