Failed to join any instances

I keep getting this error message when I try to enter The Forbidden Sanctum. I've tried doing other things like running the labyrinth, going to the hideout and doing side quests which all work fine but whenever I go back to The Forbidden Sanctum it just says "Failed to join any instances." I tried logging off and waiting and closing the application even tried different servers and reset my network connection. Nothing.

Bug Report ID: #37,620,106

Help (and thanks for the great game GGG),
Skratchez#2594