Since the connection network is unreliable missed connections are frequent. It sucks to lose your event energy because you hit way above your level and your arranged backup couldn’t get in the battle.
Please add to the “Battle starting in x seconds” loading screen an abort button that can be pressed if your backup fails to join and will cancel the attack before it starts.
This should mean that the dragon does not need to heal and event energy/boosts/items selected are not consumed and are returned to your inventory.
This same effect can sometimes be replicated by swipe closing the game, but the results are unreliable (depends on how far along it was when you closed) and you have to reload the game. I’m suggesting making it officially sanctioned with an abort button that works every time and takes you back to the home screen rather than forcing you to reload the game.
The abort button should be available during the entire “battle starting in x seconds” screen and maybe 1-2 seconds into flying your first dragon, then it will disappear.
For wars, if a defender has joined and the attack is aborted then it should still count as a successful defense to the defending team. That will prevent abuse by repeated aborts trying to get no defenders.