Items disappearing from inventory

A while back I had all my sims lose everything in their personal inventory. What I had done was I had unmarked the household as played, and if memory serves me correct I think I had deleted my cache files as well. At first, it took me a bit to figure out what was going on, and I tested it a couple of other times to see, and the results were the same.

I'm not saying this is what is going on in your game, but that was what happened in mine.