sims 4

@michlyntyres  I've moved your post to the Sims 4 Game Info section.

@michlyntyres I have not had this specifically happen, but if the sim is not in the other households it may be a sim that the game has culled and that fact has just not caught up with her yet (or may be bugging her out if she's on your lot). You could try moving the cache file and doing a repair to see if this clears the sim out.

• Exit your game then exit Origin. Delete the mods folder and the localthumbnailcache.package file in your 'The Sims 4' folder and restart the game.
• Then run a game repair [ Open Origin, click 'Game Library' then right-click Sims 4 > Repair Game ]. Make sure to let it run until it has completed all repairs (it will do the base-game first, then run through each of your expansions/packs). After that, please see if the issue has stopped. 

If that does not work... do you have Mods &/or CC?

Gallery ID: SheriGR
I play on Mac with aging off, never use Mods or CC, & have played since Sims 1.
I own all packs, run updates immediately, backup daily, & build ...a lot.

@michlyntyres, in addition to what  @SheriGR has suggested., and if you don't have Mods or Custom Content in your game, then you can try the following:  

1) Introduce your Sim with the strange Sim (if you can), so they are in their Contacts list, if you have not already done so.

2) Travel somewhere off your lot that requires a loading screen, such as another neighborhood, and when asked if you want to travel with anyone, select the Sim that is stuck in your house.

3) Once at the travel location (like a bar, museum, park, festival, gym etc.) you can send your Sim home by clicking on the house icon in their portrait. ( If you select to travel home via the map, the strange Sim may follow you home). 

This may or may not fix your problem.  It has sometimes worked for me, but not other times. Still, it is worth a try!   Basically, you are inviting them out to ditch them !  🤨😃

Please update us on your progress ! Best of luck! 🤞