An unexpected disconnection has occurred (and rolled-back)

I did the Labyrinth trial, picked (actually good gems from the fountain), and a few seconds later, while going towards the Class Fountain the game crashed and rolled-back, what looks like, the whole trial run.

(From the Paris realm)

instance server crashed, GGG automatically gets crash logs for this.

since instance server crashed there was no data to report to the game servers, so not quite a roll back.

It's not necessarily a rollback, considering the game servers' view, since they never got the data, but it's definitely a rollback from the user point of view!
And I'm not sure that it was a crash, it was a disconnection from the server, as it was said.