All unique items including the Auric Amulet in Hellfire are subject to occasionally morphing into something nearly worthless when taken to a new game. This is a bug that has always been in the game. I "test" unique items before attempting to take them to a new game to be sure that they will survive, if not I vendor them. That is to say I start a new game check the item to see if it has changed and then reload my game. In my experience if an item morphs there is nothing to be done, if it doesn't morph it never will.
One can use Ulmo's Stash (see the thread so named) to bypass this morphing possibility.
I think the same thing happened to me. Griswold's Edge, the unique sword, was gone when I started a new game and in its place was a small bottle of mana where my sword should have been. To make it more interesting, when I put the cursor over the mana, it highlighted the stats for the Optic Amulet, which I also had in the amulet spot and it did recover.
But the sword was gone...very frustrating.