Ok so far so good. I will toss in some more question to find source of problem.
You are using ServerTravel ConsoleCommand right? Do you have “Seamless Travel” enabled in GameMode Default Settings? If yes, would you mind turning that off and check if it is working then?
If not, can you print DisplayName inside of both PlayerControllers on BeginPlay and double check that, after ServerTravel, PlayerController did not update? best would be limiting this to Server versions of PlayerController by using a SwitchHasAuthority node (: