In multiplayer campaigns end of turn the campaign endturn button cannot be pressed and everything essentially freezes. This happens in these situations and can be replicated every time:
-One player is playing as Imrik and Imrik has been given the choice to confederate Caledor.
-One player is Markus Wulfhart and has reached maximum hostility for the first time
-One player is Malus Darkblade and has been given the choice to give up his settlement in Naggarond or to keep it
Essentially these 3 factions cannot be played in multiplayer campaigns. I hope you will fix this soon.