Same issue when starting a new flight from gate 30. No stairs to connect to the aircraft...
I think is something we can't change for now, unless Asobo fixes it. The issue is:
- If a parking spot is flagged as Ramp ( which can only be GA, Cargo or Military ), it won't expect a jetway, so it will use stairs instead. However, if a parking is flagged as GA, you'll see small GA AI planes instead of airliners. Users will surely complain about that, since seeing GA planes on airline gates is the first thing you notice.
- If a parking spot is flagged as Gate, the sim expects to have a jetway. Earlier releases of the SDK *prevented* developers to create a Gate without a jetway, the editor flagged it as an error and refuse to compile the scenery.
These two issues made impossible to create a proper "Apron" parking for airliners only. It was always like that since FSX but, in MSFS you notice it more, because there are more services are available now, like passenger stairs. Some developers asked Asobo to fix the editor, and allow Gates with no jetways, so now the compiler gives a warning instead of an error, and accepts the scenery as valid, but I guess the sim is still considering it as it "should" have a jetway, so it won't create stairs.
It might be possible to improve on this by using custom service definitions but, the SDK documentation is woefully incomplete here, and the relevant options in the scenery editor don't do anything yet, so we rather wait for either a fix or a completed documentation, before making changes in the blind, for something that is likely change anyway in future updates of the sim.