Twice in the past 24 hours my Ackbar's leader ability has not activated. Once in Challenge, and once in cantina battles. I'm pretty sure it's happened before too, but I know it has the last two times.
I will stealth Leia, and Ackbar does nothing but stand there with his hands in his pants. Leia's and Ackbar are the only Rebels on the team and in both cases, neither had any buffs (though that should be irrelevant I'm guessing. Also, neither time was her stealth after his Tactical Genius (which also shouldn't matter I think).