We tried contacting the server admin. Maybe we succeeded? Earlier, site updates.duplicati.com was returning a 502 error as described in the old forum post. I didn’t keep a screenshot, but another view was:
Duplicati.Library.AutoUpdater.exe check
Error detected: System.Net.WebException: The remote server returned an error: (502) Bad Gateway.
at System.Net.WebClient.DownloadFile(Uri address, String fileName)
at Duplicati.Library.AutoUpdater.UpdaterManager.CheckForUpdate(ReleaseType channel)
No updates found
(but now)
Duplicati.Library.AutoUpdater.exe check
No updates found
Interestingly, the alt.updates.duplicati.com server was up before but the download page ignores it.
My JavaScript isn’t good enough to devise a fix (any web developers around?) but another complication would be that https://alt.updates.duplicati.com/beta/latest-installers.js returns links for updates.duplicati.com which was the failed server, so an actual download attempt might have failed.