Make sure your system meets the Minimum Requirements as well as the slightly higher recommendations from MTS.While a fix or workaround are still being sought, there are some things you can do to help prevent the issue from occurring in the first place: StoryProgression is also the cause of messed-up Relationships and Aging. The missing or having clones while traveling to and from WA Destinations is due to the buggy EA StoryProgression.

The most common cause for the Missing Sims bug is according to Twallan a 'Missing or wrongly referenced outfits' issue.

Upon traveling, Sims' ages get messed up.

Or you suddenly gain a new family member or acquaintance

Upon traveling, you lose relationships with those in the Relationship panel.

Upon traveling, from patch 1.22 onwards (with Generations release), you may also get clones (aka doppelgangers, as some call them) of your Sims.

None of the keys (F1, F5, or F10, etc) works.

Click to enlargeUpon loading a save game, you find the HUD panel missing, and there are no Map Tags.

Sims 3 sim is invisible