I'm not too sure what the issue is, but after you check the monitor resolution with sys_metrics(0) and sys_metrics(1), run some code to see if it's a compatible size for 3dgamestudio to render it into fullscreen. It if doesn't match one of those modes, set it to fullscreen window mode instead by making it a borderless window.
video_set( game_resolution_x, game_resolution_y, 0, 2 );
video_window( vector(0.1,0.1,0), vector(sys_metrics(0),sys_metrics(1),0), 1, "Fullscreen Window");
Not sure if this helps, but based on what you've described, that's the only idea I have as to why fullscreen won't work for certain users. You could also try setting screen_size.x and screen_size.y to see if it corrects the issue.
