I starting a new quest with my Level 27 crews. Just two characters.
I'm having this problem for the second time. I quoted this comment because I have a suspicion that it has to do with the level of the characters. My old party had reached level 26 when I had this problem, so I was forced to close the app and then, maybe because of my number of characters saved for Quest Mode, I lost the characters of that party. So I learned the lesson and deleted the excess of characters and started the Quest with a new group. Everything went well until today, when I finally reached level 26 again... only to face the same problem. At least, deleting the characters was a good call, because when the load screen freezes and I close the app, I can go back to Quest Mode and choose the same characters.
As for the details of the trouble, I don't know if it works the same way for everyone: my case is that after I finish a quest, manage my decks and choose the difficulty for the next quest, the game simply freezes in the load screen, so that I have to close the app, open the Quest Mode and choose the characters to play again.