The amulet has 2 potential locations depending on the order you do things.
1) Gut's chambers in one of the containers (I forget exactly which one off the top of my head, but it's always the same one. Unlike the bunch of health potions and the "Lots of things" loot pile which can vary)
2) Ormeluum's shop. If you proceed to the Underdark before taking out Gut and looting her chambers, it will magically poof itself into Ormeluum's shop, necessitating going to the tower and grabbing the potion ingredients before you can get it.
Presumably, this is done as a means to enable you to access it even if you don't "Persuade" Gut to let you loot all her stuff. As it can be a useful item to have.
Personally, I find it very annoying as I often dip into the Underdark to pick up some items from Blurg and Derryth. So it gets shoved onto Ormeluum mere minutes before I go ransack the Goblin camp.
Meanwhile, it can be handy for actually accessing the tower to get the ingredients needed for Ormeluum to open his shop. (I honestly don't know why he won't open his shop to us before getting the potion. Like, clearly we're on good enough terms to go through with letting him probe us, but not trade? It also sucks you can't finish his quest and just say "I don't care about your stupid ring, you can keep it" you either have to pass some checks to take it or say you'll come back later for it. The ring is useless so I just sell it back to him anyway regardless...)
I mean, they could have just kept it in both locations. It's not like it would have mattered much if people were able to get 2 copies of it. It's nice but it's not like it's gamebreaking to have a once per long rest Misty Step cast (At the cost of a amulet slot)
