I’ve had several issues with the game crashing during Grand Arena and it is always right when I hit ‘Battle’ or one time it was just when the battle loaded. In either case I have never experienced it in the middle of an arena battle.
The problem (beyond the obvious crash) is that you hit battle, it crashes, and it counts as a battle attempt and you lose your squad without ever having used them.
Is it possible to not count a battle until a character on the player’s team takes a turn?
This might help alleviate some of the issues with the crashing for grand arena.