After using three consecutive times the standard interface to update the Sailfish OS, I try to look in the /var/log/systemupdate.log.
The update was stopped because of Alien and Co problem. Then I switched off the alien Android (from the settings menu) and restarted the update.
It works! Still work in progress at the moment, but before just after the "Sailfish OS" and odometer white bar at the beginning (<5%), I received a message saying ~"update impossible try later". Then I had to restart from the download part. So quite long tries!
Now I'm at 98% done (on the "SAILFISH OS" white bar).
I hope it could help some of you! Best regards Thoric