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[Aldora]

Did you by any chance go into E10S or one of the later ones? Once you step into the next fight, before clearing this one, you'll forfeit your chance on this one. I believe the game also mentions this when you queue up for one of the later fights, although i'm not 100% sure.

This is a system that's in place for the current raid tier of the patch cycle.

Other then that, the only thing i can think of is that your trying to queue up for the fight and the option "Duty completion" was turned on (meaning that you had to have the fight cleared before you can queue up with the current raid / pf settings).