I’ve tested this a bit, and think that if you don’t have any saved deployments when you are in a challenge and try to save it the game crashes. You have to go to “battle” save a deployment, and then you can in Challenge mode.
I’ve had this crash consistently, too.
I think when in the Challenge mode the game can’t create the save folder for challenges. I manually made a folder for a map I had not done, and the crash went away.