What you were expecting to happen, and what actually happened:
Whenever battling with an Adana team per the Campaign, I get the Server Error: Cliffy##########. It doesn’t matter which city I try. I can battle with any other team with no problems. I have tried with the Banner of Progress and with a different banner for the team.
My expectation: to show the victory screen and the rewards, not to get the Server Error.
How often does this happen? When did it begin happening?
Occurs every time I try to battle with an Adana team. This started today. I have tried with the Banner of Progress and without, and it doesn’t make a difference.
Substituting me with another Adana troop fails to cause the error.
Steps to make it happen again
My team consisted of my character as a Mechanist, Sparkgrinder, Carnex, and Tankbot 2000. It appears that the player must be one of the team (not sure if the class makes a difference). It looks like a bug with the player character meshing with the event.
It only happens once you defeat the opponent team? That suggests it’s related to some campaign counter having difficulties updating. Wild guess, which level is your Mechanist class (the level you upgrade with souls, not the champion level)?
I have opened a ticket via the website you posted, as well as two others because the issue is getting worse, occurring with more and more hero classes. Oracle, Shaman, Priest are also not working. I am getting no response to these requests for assistance, not even an automated response except for the first one.
This issue is making the game unplayable for me, which is quite disappointing because the game is one that I have come back to after several years and found the expansions within the game interesting and appreciated.