I have found that on one of my characters the quest "Banish the Banished" within the dungeon "The Banished Cells I" is unavailable to me. The quest giver at the start of the entrance does not have the quest for me. I do not have the quest in my journal, and I'm sure I have not completed the quest in the past. I have attempted to obtain the quest solo and also in multiple groups. I have tried to relog, restart, and use /reloadui and have not had any luck. It seems as though the game thinks I am currently on the quest, but it does not progress and is not in my quest journal.
I've had a support ticket open for the issue for a week or so now, and am reaching out to try to find solutions in the meantime.