Black Lion Salvage kit disappearing
Did some additional testing with regular salvage kits: It happens if you salvage in bank view and not in inventory view.
as someone on reddit noticed: it gets put in bank instead and does not disappear
Remember, any time you double-click on anything in your inventory that shows when you have the Bank Vault open, it is moved to the Bank.
Yup, double clicking any item either on inventory side or bank side in the Vault panel will move it to other side (bank to inv, inv to bank, vice-versa)