Ok, so after a lot of waiting time (4 days!), waiting for a call from my ISP, they confirm everything is OK on their side, and they remotely look at my port forwarding configurations in the ISP box and they validate it.
Indeed, when browsing through another network (tried Tor, mobile data), entering my IP directly reached the servers then redirects to
https://xxx.xxx.xxx.xxx/yunohost/admin
With an “Unable to connect” error on firefox-based browsers.
Any clues on how to diagnose/fix this?
Diagnosis is still:
Port 443 is not reachable from outside.