Hi. I have a lobby in my game where all players gets conneted to. After the Server presses Start the server executes a console command (ServerTravel) wich loads the gamemap. I create the UMG widgets in the Player Controller using OnPostLogin(in the gamemode) to trigger the event. The problem i found is that when using ServerTravel OnPostLogin(in the Gamemode) is NOT Triggered. What am i doing wrong and how can i fix this ? Is there another node that gets called then a player enters the map ?
Just in case your problem still exists, this might provide a solution for you:
Post Login Event not firing on active clients after Seamless Travel
I stumbled across it, just a few minutes ago, having a similar issue. 
OnPostLogin is only called, when a Player logs in. With non-seamsless the player are disconnected and connected again, when you use ServerTravel. Thus, OnPostLogin is called. But with seamless travel, the players stay connected and OnPostLogin is not triggered…