
Save often, and rename each appropriately so you know which is which.
If you have World Adventures and plan on sending your sims on vacation, make extra backups of the save using "Save As" to save the game. If you find Sim(s) missing during gameplay, "Quit Without Saving" Yes, you will lose progress, but the alternative is losing the game entirely. Try NRaas Story Progression, or AwesomeStory Even if you uncheck the box to disable it, it may still be running and corrupting your game.
EA Story Progression is the default when you install your game.
Do NOT use EA Story Progression especially if you have World Adventures. Those that tend to stick with one family (don't switch active households) tend to have less issues and problems. Run the game from admin user account or with admin privileges, doing so helps eliminate many user related issues. Make sure your Graphic and Audio Drivers are up to date, DirectX is up to date, and close all unnecessary programs running in the background (some even disconnect from the internet). 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.