Have you changed the AFCAD that comes with KLAS OR you have another AFCAD in conflict ? If another ACAD is in use by FSX, the GSX airport customization won't be loaded, which will make the Safegate disappear.
To know which AFCAD is in use by FSX (and thus GSX), open the "Customize airport positions" menu from the "Couatl powered addons" menu, this will open the GSX scenery editor, that will list the AFCAD currently used.