two friends of mine and myself are trying to play together in a multiplayergame each time a new update comes up, but everytime, we had the same issue. The scenario is as follows:
PlayerA starts the game, PlayerB joins and finally PlayerC. The arrangement doesn't matter. As soon as the third player joined (he completly downloaded the map) the screen for him turns black and the game hangs up for the others. We don't know what the reason is, but we found a work-around: deleting the files in the temp-folder and restarting the game helped. After that, we could play together for some time (about an hour until it appears again). We are 2 Windowsx64-Users and 1 Mac-User. The Mac-User appears to not have such a temp-folder, so he didn't do anything.
Maybe this information helps you, finding the bug

Greetings,
Schorty