We are actively monitoring for bug and issues with Grand Arena. Please post your ally code and what issue you are experiencing. Thank you for your time!
Current Grand Arena Known Issues:
There is a rare chance the first time you attack a territory with no defense will cause the client to restart. You will not receive rewards or Banners for this battle that crashed but you will receive Banners and rewards for subsequent battles after the restart. This is not impacting all players but we are still investigating the issue and let you know when we find out more information.
Error 11 causing reboot of client after first win - patch is deployed