Regularly, at least 50% of the time, the game will freeze for myself and my husband (I am the host on our home network) when we try to go through a portal to another realm or fast travel to another realm. Instead of the typical loading screen, all we see is a black screen. Eventually we have to completely exit out of the game using either Task Manager or Stopping the game through Steam, then relaunch to try and travel again. Gameplay at any other time is usually okay, without stuttering or lag.
I have figured out the issue and workaround. If my co-op player(s) go through the portal first and I approve it, all is fine. If we go through together or I go first, the system is trying to get me to "approve" their travel while I'm on that black screen and it locks up because I can't see the request to approve it. Still a bug, but you should be able to fix it now.