Just adding to this thread as we had the issue. Sadly we only got off the initial tutorial bit and then shortly after he got disconnected (it presents itself by also disconnecting the party citing a network issue - though we know that's not actually the case).
I was hosting.
My friend was trying to join, it would show as player joined - then [username] left.
We managed to get it working once by deleting his save data (local/cloud) though obviously this is a rubbish solution if he wants to run his own single player campaign (which he does). Might see if he can get it saved on a USB just so we can play but it's bit a real spanner in the works for us.
A 2nd time it happened after the next reload attempt, only he cleared his save data (local/cloud) and he couldn't load in. I cleared my cloud data when it worked, not sure if it was needed or not.
I also cleared my cloud data as host, we're going to try again later and i'll try to clear my cloud data and he can clear all his data, but really hope Larian can jump on this one.
