The way I understand the OP, the error goes away if VPN is disabled, strongly indicating that the VPN is doing “something” that does not work. Most often this is caused by DNS problems on the VPN.
Also, I think this is a smoking gun:
With split tunneling enabled, netstat does not return anything.
Additionally, a Google search indicates multiple cases where the error message was related to DNS issues from the provider.
There are also some with Socket.Bind, but you can see in the trace that it is using Connect and not Bind.
The netstat non-return probably is seen below, i.e. it’s not simply a bare netstat:
and to me this suggests it didn’t connect, but it’s unclear why that would happen.
The netstat command should not be trying to slowly DNS-reverse the addresses.
With that clue, I found at least one where 0.0.0.0 was returned. I didn’t look much.
It can also happen on the remote address of a connect, per web search, and docs:
Look at error. Mine seemingly resolved the remote, but (by its design) page isn’t there:
Jan 24, 2025 10:30 AM: Error in updater
System.Net.Http.HttpRequestException: Response status code does not indicate success: 404 (Not Found).
at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
at Duplicati.Library.Utility.HttpClientExtensions.DownloadFile(HttpClient client, HttpRequestMessage request, String filename, Action`1 progressReportingAction, CancellationToken cancellationToken)
at Duplicati.Library.AutoUpdater.UpdaterManager.CheckForUpdate(ReleaseType channel)