It loads the default level. This is were I hooked into this bug and my dirty workaround is to change the default level before changing the map on the server. Possibly loads the map two times but better than no map change at all 
Add this to your GameInstance and call it in the Blueprint before you change the map on the server:
.h
UFUNCTION(BlueprintCallable)
void MySetGameDefaultMap(FString NewMap);
.cpp
void USCAdvancedFriendsGameInstance::MySetGameDefaultMap(FString NewMap)
{
// Really ■■■■■■ workaround for 5.6 server travel loading always the default map instead of the actual map we want...
// Expects REFERENCE to map ("/Game/Maps/Map_Development.Map_Development") not only map name...
const UGameMapsSettings* GameMapsSettings = GetDefault<UGameMapsSettings>();
GameMapsSettings->SetGameDefaultMap(NewMap);
}