after playing the game for tens of hours with friends online, I can no longer join or be joined by a friend or even go to multiplayer because the button is grayed out with a padlock. I didn't do anything special and I already reinstalled the game 3 times but it doesn't change anything.
The only thing I did between the moment I could play and the moment I couldn't play anymore was to download workshop maps on steam (I don't know if it has to do with).