I was doing world quests in Azj-Kahet and the moment I finished the last one required to unlock the Special Assignment I heard the “objective failed” sound effect and my chat box displayed a message saying I had failed the Special Assignment. When it was locked, the Special Assignment world quest was on my map. Now it’s gone.
Earlier today I completed some dailies in Dorn, completed the Special Assignment there, and received a Seasoned Adventurer’s Cache, so I was under the impression that I’d be able to do the same in Azj-Kahet.