I have experienced this issue as well, and to be honest I'm quite upset about it at the moment. Previously, only things like Plasma packs, homework and upgrade parts have disappeared. Which is completely annoying, but replacable. Today, I also lost some Death Flowers and masterpiece paintings. Which I'm absolutely not happy about. One sims inventory was wiped clean. He had the most items, including a bunch of paintings. I got so mad I quit without saving.
- Do you play rotationally ? - Yes, but not the last days.
- If you do, did you have a flea market happening while you were playing another family ? - I haven't played with another family
- What were you doing when you noticed the stuff missing ? After a vacation in GF or S ? Did you travel with your Sim ? - Sims came back from work
- Are you playing an kind of active career ? - Yes one sim is a detective, and the inventory items were missing after the sim came home (the detective inventory was intact). I always do a round to check everyone (because sims will never do anything remotely useful while you're not watching, so I have to give them something useful to do), I noticed right away that at least one sim inventory was wiped, the others had minor things missing, like the teen didn't have his homework.
- Which items (type) do go missing ? Only collectibles or other stuff ? - I always have basements where I place paintings and collectibles on "display" or in chests. So I keep those things out of personal/family inventory. What usually goes missing is upgrade parts, medicine, and if vampires, Plasma packs. I usually buy about 50 packs for them each, but I've given that up. Really can't be bothered buying them constantly, because we can't just type in a number, but rather click the arrow.
I really see no other alternative than to take my sims off their jobs, and never travel anywhere until this is fixed. I've had this issue for a while, in different saves, but never had a sims inventory cleaned out like this. Really upsetting.