Please see the pinned post: About the Vermintide 2 - Technical Support Category to see what information to include in your report.
Me and a friend on Xbox One have been playing vermintide 2 for about 2 weeks then all of a sudden he can’t join my game and I can’t join his game we both get eternal error messages. We have gone through the technical support read all the other posts and have done what they said we have changed ports we have uninstalled the game reinstall the game close the game open the game we’ve done everything that is possible and still have the problem.
It’s ok. I don’t need a refund, I’m still enjoying the game. So we tried something yesterday that had a little success…
We got one of our other friends to download the game and he acted as the host for the 3 of us. Not me and my original friend we able to join him and successfully play together.
The internal error that both me and the original friends are getting only seems to happen when we try to join each other directly. We also noticed this problem only started after the last update that we got on Xbox on the 7th of June.
Hope this extra information helps even if it’s to help other people