Very interesting and plausible explanation, thanks Umberto.
I will continue my investigations, like this morning, where I tried a LSZH>LSGG flight. I started cold & dark in terminal E, on a medium location. Had the jetway who retracted for no reasons. I thought it was just the very well known Asobo bug, but it was not ! The gate was effectively retracted (not just visual), because after, the PAX didn't boarded, while the baggage were loaded normally ! In Geneva, I used gate 42 (was free), but when I selected deboarding, the jetway didn't come and when I called it manually, the support with the wheels goes up side down. Something I saw already quite often in LSGG.
I must say that I start to be really fed up with this MSFS ! We spend more time in trying, investigating problems than in really flying with pleasure !