Os android
Wi-Fi of a school
Message sending gets no healthy network error.
No incoming messages
Is access to the Internet moderated?
Good point. It can be that they do not accept self signed certificates and non standard ports.
If you go to Settings > Advanced Settings > Record Logs (click on download icon) you can get the log downloaded to OneDrive or someplace where you can download it from desktop and see what’s happening. Maybe it’s an MTU issue, maybe they block certain types of traffic, maybe they whitelist sites, etc…
Actually I now know a case that it happens also from a standard home Wi-Fi setup, but I have no access to debug. In any case it seems to impact more users than expected.
but I have no access to debug
I mean client-side debug logs.
Settings > Advanced Settings > Record Logs in xx Messenger has a small download icon where you can get client-side (not WiFi-side) debug logs. They contain some confidential information so remove those details if you post it here.