Thats why i’m asking if you maybe write your own code for that, as you cna od that 
Then i dont know whats wrong, if you pick default pawn defualt spawn system should use this pawn exclusivly. You might try override GameMode functions which selects Pawn which is “GetDefaultPawnClassForController”. Place to PlayerStarts. Maybe it indeed replication problem, but it kind of not make sense as GameMode class runs exlusivly on server and it spawn objects in server state which is replicated to clients