WebRequest returns undocumented code 1009 with error 5203 for one domain only

[Ta Hai Shen Yuan]

WebRequest() returns 1009 with GetLastError()=5203 for one domain in a newly installed terminal. Another terminal on the same VPS reaches that domain normally. A plain GET script on a live chart gives these results:

Results:

Terminal A, build 6295, newly installed

  my-server.example (2 URLs)  res=1009 err=5203  no body, no headers  0-16 ms

  www.google.com (https/http) res=200

Terminal B, build 6230, same VPS

  all of the above            res=200

build 6296 clean install, Windows Server 2019, other VPS, 10 other terminals running

  my-server.example           res=200

PowerShell Invoke-WebRequest to the same domain on the failing VPS returns 200. The domain is IPv4 only.

Questions:

1. What does return code 1009 mean? I could not find it in the documentation.

2. Is there a log or setting that shows why the terminal fails for one host only?

3. Did WebRequest connection handling change between builds 6230 and 6295?