Ideas
I've been using Manage Worlds to fix it, but if I select Save and Manage Worlds, it locks up the game.
I've noticed it happening frequently since the Enchanted expansion.
I've played Sims games since the day The Sims was released, and this is by FAR the most frustrating thing that's come up. Every time it crashes, I have to repair, and because I have every pack ever offered, it takes forever to get back to my game, often only to have it start stacking up actions and the Sim just freezes.
It often happens to only one Sim in the household and the other remains playable for a bit, but then that Sim locks up, usually from trying to interact with the frozen Sim. Sometimes if my fairy has a sub-action of walking, I can click the walk to end it, and the Sim goes to the next action, but skipping the one that was supposed to be in process. My DOG even freezes up. (Not to mention if I pick up my puppy, I can't put it down, causing its needs to deplete. It would die if I didn't restart the game.)
PC, no mods, no CC, all packs installed.