- I am only being offered one item from the Great Vault and it's one I already have.
- The Great Vault is giving me a duplicate item of one I already own.
The Great Vault will never offer you two of the same rewards simultaneously. If you unlocked more than one reward this week, all rewards will be different from each other.
The Great Vault can offer you an item that you already own, or an item that was already offered to you in previous weeks. This is not a bug. If none of the rewards suit you, you can choose a token reward instead which may be redeemed at vendors near the Vault.
Note: The pool of rewards you can choose from depends on the variety of content you have cleared. As an example, during the Shadowlands expansion, if you have never killed Sylvanas, you won't see loot from Sylvanas' loot table in your Great Vault. To increase the pool of items you will be able to choose from, play new, different content.