When GSX can't show passengers, usually because the jetway hasn't docked correctly, it will show a message on the top part of the screen.
A message that you might have missed, if you use the menu incorrectly, by closing it and reopening with the mouse instead of opening with the mouse only the first time and then always using the hotkey or the x icon to open/close it, as suggested in the manual. One of the side effect of using the menu in the wrong way, in addition to have to double click every time, is that you'll miss those text messages when GSX is trying to tell you something.
