Were are you testing the airplane ?
If you are on a gate with a Jetway, by default you are only supposed to see the rear stairs and, if either the airport profile has the "disable stairs" option enabled for that gate, or you set the option to always disable rear stairs on gates with jetways in the GSX Settings, you will never see any stairs.
That's why it's best to test a configuration for stairs in a parking on the apron, with no jetways.