Server travel - clients disconnect

Server and clients can get connected in a level. On command, I want the server to switch to another map and all clients should go with him. This project will run on both Desktop and HTC Vive (i.e. with SteamVR), based on the MultiUser Viewer template.

So, I tried to do a Execute Console Command “serverTravel NewMap?listen”, without seamless travel. The server travels, but the clients get disconnected. (both Desktop and VR)
When use seamless travel is set with empty transition map, server as well as clients join the NewMap, but they don’t possess their pawn any more (I guess, as in Desktop view, you can’t move, VR only head movement)

What am I missing? Shouldn’t the clients follow, when ?listen is set?
How does seamless travel work? Does the transition map have to be blank or has the GameMode to be set to the one that is used in the other maps? When the new map is loaded, what has to be spawned anew (as e.g. the pawns don’t work anymore)?