Nothing has changed in the GSX update, when the passengers is going fast, it's ALWAYS due to the jetway not being connected, which usually means it hasn't been detected as docked.
You just need to be sure that:
- You disable the automatic jetway connection in the Fenix EFB
- If you are using the SU10 Navdata, and the gate you are in has DOUBLE jetways, sometimes it's impossible for GSX to detect the correct jetway, because it sees two jetways with the same name, and the static one might be the closest to you, but since the current Navdata doesn't give us the jetway position, there's no way to fix this, until the Navdata update, scheduled for SU12.
In the meantime, the only way to be sure that gates with double jetways are always detected correctly, is to Disable the SU10 Navdata and use the airport cache, because when we read the .BGL, we DO have the jetway position. However, that won't work with Marketplace airports, of course.