I ran the latest update and the passengers are still in the cabin. Gate 12 LIRN with Menzies handling. FSLabs A319.
Your problem never had anything to do with the issue discussed here, which was a specific problem with the smaller staircase that are used only on Dash-8 or smaller planes, and this caused GSX to freeze entirely.
I reset the position and tried again. This time the crew bus arrived and six ordinary passengers (not crew in uniform) got into the crew bus. This bus departed and another crew bus arrived. (I'm typing this as I watch). Bus doors open. 4 females cabin crew disembark followed by Captain and First Officer. Crew Bus departs
This only seems to indicate the passenger number was too low. With the FS Labs, it's the airplane that controls the passenger number and communicate it to GSX. I believe FS Labs have said on their forum this process is not entirely bug-free, so a fix from them should arrive.
However, if you disable the "Estimate Passengers Number" option in the GSX settings, you can override what the airplane might have sent to GSX.