Ultimate Rank in 3T and triggering an essential event

[cornfielder]

I've managed to get all three ranks in ROTH and OLB, and I've got 100% and Speed ranks in 3T, but I can't get ultimate. For some reason, I just can't figure out what triggers the particular event (not posting spoilers here...) that needs to happen to get the last two crystals. I know it happens after beating all four elemental dungeons, but you can't do that and get ultimate... I've only managed to get the event early once before, the one time I got speed rank, but it happened by accident; I have no idea what I did to cause it. A little help, please?