@LessaMarieIf you have any mods and CC move your mods folder to the desktop.
Go to the Documents\ Electronic Arts\ The Sims 4 folder. Find and delete "localthumbcache.package" file and all folders with the word "cache" in the name.
Then open Origin/ My game library, right-click on TS4 - option: Repair
You have to wait until Origin will fix all packs - not only the base game.
Then launch the game. Check if your sim is visible now.
If this error still occurs go to Management Family Panel and move your family to an empty lot. Check if your sim is visible now and you can control him. If so - move this family back to their home.
I don't work for EA