Were you in the wilderness or just your res.? Also, have you given, as Michael_Nolan said, anyone a flag for your residence? Like a container flag, use flag, etc.
This. I highly think it's this reason. Listen, there are people in this game who will steal stuff even though their "trusted friends". Be sure to always remember your permits and reset them shortly after the person who borrowed the permit. Don't end up having a tragic ending like king_redbird. He was grieved by players whom he trusted. I made some friends in-game that really treat me as an honest person. I tell them, I don't mind if you reset the permits, just so that you are safe from "worries". I don't grief, but if they deem is necessary, then they should.
So, dude, you WERE on your residence? You weren't out in the wilderness, or on someone else's residence, maybe?
This is just my 2cents and when I first started I could have been a victim and I see this every now and then in game but it goes like this: Member number 1 comes in and claims a plot of land. He then takes the time to build several houses/rooms and then has others "rent" from him or offers to let people live there for free. He provides chests, beds tables etc. for them. That then means he is able to access their stuff since it is his plot. Now if he has done that and given others flags then everyone living there has access to anything on that lot. If they wanted, they could go to your chest and remove your items. If this is the case then I encourage you to claim your own plot and put your items in a chest there/live there. If it's your plot and you did in fact give flags then I'm not so sure there's anything you can do other than remove them and not add anyone unless you know them again.
