The above bug actually often appears.
Not just in my game. Also other guild members told me.
I want to make progress in friendship campaign and it works for more or less steps. Maybe one maybe more.
Then the next doesn’t work, i get the above error, in my language (i just translated into English). And the progress isn’t counted too.
The result is that I’ve to break with the campaign, do sth else in the game. When I come back, usually the next step works, but only for one. Then it break again…
Other members said they needed to restart the game.
Is this bug already known and anyone working on it? 
Occurs often. Not anytime, but often.
I wanted to report here cos with the last update it haven’t been fixed.
For you all a nice day. Regards