Hello, i am having the same problem, we are not using any mod, we started playing a GM campaign i downloaded from workshop and it worked fine yesterday, we are using Direct Connect as two of us have the GoG version, and today when trying to load the campaign i cannot get the players to connect, a message saying "installation 100% complete" appears for them and nothing happens then.
I have tried then to just create a new save and again same error and unable to join the game, tho me as game master i see the "player join" message when they try but they cant do anything else.
Please help we were having such a nice game :)