Did not receive dungeon loot from end boss

Character: Stixnstonez
Whitemane Cataclysm Classic Horde
Item not distributed: Souldrinker
Dungeon: Stonecore (Elemental Twilight difficulty)

I was in a premade group using the dungeon finder tool. We completed the Elemental Rune dungeon and loot was working fine (something drops, we roll, it was distributed and placed into our bags). At the last boss, there is a new loot table. I rolled on the LFR item that drops for the new Elemental Twilight dungeon and won the roll (I was the only one to roll). I saw that I won the item and left the dungeon group (even though were all in the same group outside of the dungeon).

The item was not in my bag. I used a search tool and was unable to find it. I checked the chat window and it said that I had won the loot (as the only roller and I used “Need” to top it off).