The only common thing I've noticed from people who get ??? items on this server is they attempt to transfer items. I'm not sure if it's before or after a game. I know you'll take care of it for the user, but even with their corrupted data (which I looked at), I can't find out what causes this problem to fix it.
Really need people, some time, to come up with a way to generate this bug 100% of the time so that I can fix it in the source code. For that would be a glorious day!
I'd just recommend people NOT to transfer, but if you're going to transfer, I'd change server blocks, make a new game, drop the items on one char, pick them up immediately, change server blocks again, create new game, come back with new character and give items.
Pretty sure that should avoid the ??? bug on transferring items.