I beat everything with Gwen, but in the last battle I get a server connection error (320000), what can I do to get the achievement? :(External link →
This is a bug in the wild fragment conversion ceremony. It will auto resolve tomorrow morning with the client update.
To get yourself out of that loop before then, hit the little flag button on the world map to retire the adventure. Note that retire does not mean surrender - if you've already won, it just means claim all rewards and delete the in progress run. You will not get the reward popup - but you'll still have them applied to your account.