This problem seems to be a moving target, but I believe we are on to something. I am presently at the same gate H17 with the same plane A321 (FSLabs) and I narrowed down the issue to the loading of the airplane through the ATSU of the plane.
To recap:
1/ Catering requested and delivered by GSX through ATSU
2/ Refueling delivered and completed by GSX through ATSU
3/ Jetway (requested through GSX menu) to L1 because the ATSU request was not implemented on time as required
4/ The boarding requested though the ATSU never happened at the scheduled time, about four minutes beyond that time, I requested the boarding through the GSX menu and everything worked normally, I could follow the loading through the payload page.
5/ The pushback was requested through GSX and performed normally
Bottom line, I believe - but submit to your expertise - that the boarding process not happening through the A321 FSLabs ATSU could be the source of the problem since, in my previous unsuccessful scenarii at KORDv2, I was loosing my GSX menu precisely at or after (but never before) the boarding time when that sequence did not take place (including as a first sequence the jetway positioning). Considering that the three products (KORDv2/GSX2/FSLabs) are very cleverly thought and work together, and if this issue can be replicated by others, an adjustment could be needed.
Additionally, I checked the boarding sequence at LSGG, LSZH, KLAX (all FSDT):
A/ if I request through the GSX menu the boarding, all vehicles for luggage and mobile stairway for the backdoor come into position, but the jetway remains idle and the GSX menu is not accessible anymore (only the airport menu).
B/ If I request as a first sequence "operate jetway", it will get into position on the selected door. Boarding can then be selected. Is this the way it is supposed to work and did I dream that the jetway was automatically moved into position at the door when boarding was requested?
Kindly let me know if all that makes sense to you.