I only ever get special rooms for my lowest level characters. My “dream team” that I usually PVE with are all 14 now, but have never gotten a chance at their special rooms because those lower level characters are all that are ever offered. Since those lower level characters are not high enough to enter, this blockage never gets cleared.
And yes I understand you only get to complete these rooms once. My level 14s have never been given their level 13 rooms.
Is this intended? Maybe as an incentive to keep your characters all leveled evenly? Or is this a bug or oversight in coding?