In Shadowlands, Zereth Mortis, the Treasure: 65173, Library Vault it appears that you must have Dealic Understanding (https://www.wowhead.com/order-advancement=1932/dealic-understanding) unlocked to access this treasure. (https://www.wowhead.com/object=373543/library-vault#comments) Thanks for all the great work.

Exciting, a hotfix-notice. I wonder if they've done that to the other treasures with schematics that you can loot before knowing the relevant Understanding as well... :D