Unable to connect to achievement server BUG

I was playing the Copper Citadel when I got this error "Unable to connect to achievement server". I was kicked out from server and the teleports to the Citadel did not appear again.
By the way, very often when there are disconnects, it is the Citadels that are marked as failed.
It's very disappointing because the Copper Citadel is the rarest of the three one.