While doing the horde war campaign I got to the “siege of boralus” quest given by Lillian Voss. When I clicked on her, the quest disappeared quickly and there was no marker to get it back. Thinking I got it anyway I went back to Zuldazar but the next quest I need to continue is not there and it wont show up. I don’t know if I have to restart the campaign on another character or if this is just a bug that might be able to be fixed?
That quest is basically just the “unlock” for the dungeon. It’s one of those quests that immediately completes.
The next quest is “With Prince in Tow” from Nathanos. See if Tattersail has an option to send you back to the boat on the Great Sea to pick it up.