Yeah, I had something similar to this happen to me today. After a single Pantheon match, I went back to my demigod selection screen, and both Sedna and Oak were grayed out, and thus, unselectable. (Light side as well, here BTW) After another match, ALL demigods on my selection screen were "gray", effectively forcing me to play as my previously selected character, Rook.
Kinda wierd, really. I got the distinct impression that the game app was trying to tell me something...
"You'll play as Rook, and you will LIKE IT, Goddammit!! Now shut the hell up and enjoy your Demigod!" 
