This is a known Sims 4 simulation lag issue and is usually not save-breaking. The game simulation freezes while animations keep looping, which makes Sims appear busy even though they are not doing anything. This is commonly caused by a stuck interaction, outdated mod, or time desync. First pause the game and open the cheat console, then run resetsim * or shift-click individual Sims and choose Reset Object. If that does not work, save the game, exit to the main menu, and reload the save instead of waiting in live mode. If you use mods or CC, remove them temporarily and delete the localthumbcache.package file before restarting the game. You can also try traveling to another lot and back or repairing the game through the EA App. If the problem keeps returning, use Save As to create a new copy of the save, as long-running saves can build up simulation errors.