18 April 2024 UPDATE: The issue has been fixed and Crossover and Shadaloo duel are working as intended.
We have identified an issue in Crossover and Shadaloo duel (from the Ninja Operations event): users are kicked out from the battle every time they attempt to battle in this event.
We sincerely apologize for any inconvenience and while were working on a fix, please try this temporary solution: check if you have any borrowed (mercenary) units in your line-up and try to remove those. That should fix the issue for now.
If the problem persists, please submit a support ticket to us.
Thank you for your continuous support!