We had a similar problem a few months ago. luckily it was generally just glamour prisms (though it worked out to be like 5000 + prisms and the night after i put in 1500 worth of them in) but we keep our third tab open now but limit it to only 15 of each prism and them stuff like the fried fish for the summer event things that aren't worth anything and limited amounts. To long term members. new members get no access.

Unfortunately Se is correct that you as a fc have control of who can access that chest. It still be nice if se would least punish people who clearly stole even if its a warning and 3 strikes you get a suspension.