Lost item

Welcome,
After killing the last boss in the Underbog I've got an item called Doomplate Shoulderguards in an item roll. But after winning it, I didn't get it. I didn't have a space in my bag. I've checked a mailbox, but it wasn't there. What can I do, to get this item back?

usually the item is still there @ boss, so you can just free some space to loot. If you have not doen that, it is lost