Could it be possible that you didn't actually purchase any belt (perhaps it was another gear piece instead) and the roll from the dungeon went to someone else?
Dungeon roll was a need and I was the only one who rolled on it. I got the notification when it happened. No item.

Purchasing the belt, I would have still had grabbed a belt if it was by mistake because they are grouped together and no new belts were in my inventory. This was from the creation tomestone vendor. More confirmation that It would have been a belt is that I had just over 500 tomes, I would have less than a hundred left if I had bought anything other a belt in that tab and I have just over 130. Lost the tomes, no item.