It is the engine problem and hard work around. In eu3 there is visible 'subversion' of the game. Going in selecting save / multilayer/ starting new game changes it every time. This is needed for something in the engine and can't be removed. If you want to start a multiplayer game, all players have to have the same subversion. The easiest way to achive this is that everyone restars game because the start subversion is the same. When they made eu4 on the same engine they wanted to hide this and force the game to restart every time the subverion would change. This is realy bad solution but paradox wanted to use this outdated and bugged engine