Thanks Kiji! Found it. Tylus has two jobs: guarding the Zakum dungeon and starting the 4th job advancement. For a warrior already past 3rd job, his Zakum talk was taking over the whole conversation, so "Tylus' introduction letter" never got a chance to appear even though the quest log listed it as available. Now, whenever an instructor has a quest for you, the quest shows up in his menu first, with his usual talk as a "Talk about my training" option underneath. This applies to every job instructor, not just Tylus (all five El Nath chiefs, the 2nd job instructors, the Holy Stone and the Door of Dimension). It's LIVE now: refresh the game, talk to Tylus, pick the introduction letter, and he'll send you to Harmonia in Leafre. Let us know if anything along the 4th job chain gets stuck after that!