[Error Analysis] Sim can't return home

Muppety wrote:
1. Never used mods.
2. Started a new town for this.
3. Fresh sim.
4. I was able to get into graduation, get out, new trait, no problem.
5. I didn't have anybody to invite to graduation, so I didn't bother with it.

Everything was fine at university, even getting home after the first term. When graduation comes up, my Sims graduate, they get their extra trait, they're loaded into the van and the old town loads. My Sims, however, are now 'invisible' (no picture above or to the side, just empty space/boxes) nor will they do anything I ask them to do. I've tried editing town, I've tried reloading, I've tried making another household active and returning, nothing works.