As explained so many times on the forum, if the jetway doesn't connect, or connects partially, passengers will be simulated, so their boarding will proceed very fast. You think the problem are GSX passengers, when in fact your problem is the jetway itself.
A common reason for jetways not working, is not having Disabled GSX Jetway replacement files for an airport you have an add-on for. Normally, this is done automatically be GSX when installing it the first time but, if you add new 3rd party airports after installing GSX, you need to go again in the Config page of the installer, and add the new airport to the Disabled list.
This is of course explained in the GSX manual, Page 7:
IMPORTANT
The Configuration of 3rd Party Exclusion from Jetway replacement is done when doing any of the following:
• When you first Install or reinstall GSX
• When you perform a GSX Update
• If you Install/Reinstall/Unlink/Relink any FSDT airport
If you install a new 3rd party scenery, just installing it won’t result to automatically go here and reconfigure Jetway Exclusion, you should develop a habit to always check the GSX Config page after installing a new 3rd party scenery. Failing to do so, would result in Parking conflicts (visible as double Parking spots in the World Map), and Jetways malfunctions.
If you never use default airports and you always have a 3rd party add-on for any airport you fly into, you might consider Disabling ALL GSX Jetway replacement files at once, by clicking the >>> button on the Enabled side, so they will all go on the Disabled side, and eventually Enable an airport, for that time you want to use the default scenery.
This to explain the "passengers not showing, boarding too fast" issue.
The "passengers in the air" issue, instead, might be a very different issue, usually because you are not using a GSX airport profile or, even if you do, if the profile creator has forgot to set the Jetway floor heights, which is an issue explained at Page 71 of the GSX manual, no use repeating it here, because it's quite long.
I also suggest continuing reading Pages 73 and beyond, which explains OTHER possible cases of "passengers in the air" with specific types of jetways has been used, which might lack their definition in a custom GSX airport profile.
