I hate to be “that guy”, but in four of the last five dungeon queues between last night and this morning there has been someone playing the wrong class. Some of those grps broke up, some of them tried to play with folks insisting on playing the wrong class and in some folks swapped out of their assigned role to compensate for the person who insisted on playing the wrong class.
If you sign up as multiple you need check (look up at your name) the icon you were assigned.
Some of the queue problems can be fixed by the Devs by adding more filters and mechanics to the system, but until then please only check the items on the list you can and will play if you get selected for them by the queue.