I have tried exactly what you described, ie create a map in map designer, save it then open it in galaxy forge 3,yes I did see a black screen, but the scroll bars suggested that the stars were to the down and right, so I scrolled out to max view then used the scroll bars to drag the view area until I could see the systems.
so YES you CAN edit a map designer map in gal forge 3 BUT you must save the map in the program galaxy or you can not play it
harpo
