Some kind of toilet bug.

[Elyasis]

Any sim who tries to use the toilet is permanently adhered to the seat until such time as a different sim in the same household moves them both out. Then they can freely move again. Haven't tried resetsim yet for this purpose but I imagine that will get them off of it.
Any toilet. Any sim. At any time. And bloody well recurring.

Anyone else have this issue in their game?

[The_Goddess]

Nope, no super glue on my toilet.  That is hilarious.

[Sablesasha]

That's happened to one certain Sim in my game.

Her babies would even start to starve and she would be still sitting on the loo. I kept thinking maybe she was reading a really interesting magazine hehe.  The only way I could get her off was resetsim.

But maybe her hubby did exactly that, superglued the toilet seat! 

[snapzit]

I had a male Sim stuck peeing for ages. I had tried to get him away from the toilet by using moveobjects, but that really fucked him up. He disappeared and got stuck between the first and second floors of his house, carrying endless plates of food. I could catch a quick glimpse of him from time to time. He wasn't able to eat, though. He was beginning to starve and stink by the time I went back to a previous save and did the resetsim. That fixed him.

[Chain_Reaction]

I had this issue, but with beds. Each time they routed to a bed, they'd stand by it and wouldn't respond to any further commands and any sims that were previously asleep before this bizarre glitch hit would not get out of their beds. While obsessively resetting sims, I noticed the game was no longer generating thumbnails of sims, several sims had become invisible and also several sims and even my house would not render into high detail mode despite my camera being on it... then a horrible lag hit and I realized the engine had essentially had a complete meltdown and just exited without saving which fixed the issue obviously. This was after playing for many many hours, which leads to the conclusion that a memory leak caused an explosion or one of the caches had gotten corrupted. I deleted them all to be safe.

[DMDye]

The superglued toilets were happening in my son's game last week.

[J. M. Pescado]

Fixed now.