I''m having this same issue now. In story mode, the game just crashes after I choose a saved game. Cant even initiate a new game (without it also crashing). It won't even get me to the map screen. I press the 'play' arrow in the game selection screen, the game hangs up a bit and then just exits the game back to my iPad's home screen. I've tried closing and relaunching the game many times and choosing different games, etc. I've also shut down and restarted my mini. No effect. I have 23/24 characters, but have had 24 and this has never been an issue before. I play on an iPad mini 2. I was able to play a game in quest mode fine.
Here's one thing I noticed -- not sure if it's at all relevant. On the game's home screen / main menu, there is typically a boxed check mark next to the Challenges button, but that is absent. Sometimes, I'll see it flash up briefly shortly after the game launches and connects, but that's it. Does that mean anything?