Hi Umberto,
I use last version GSX2 upgraded with P3Dv4 and I have found a possible issue:
if I select first "request refueling" and after "request boarding" all is OK, but if I select directly "request boarding", after the automatic refueling and after the boarding pax the payload is always clear.
All this if is setted "Assistance service Auto Mode" in GSX, instead if it is not setted all is always OK.
cheers
Rudy