Well, I was using the same browser [Firefox/Waterfox] and settings as for all the other downloads but then I remembered, I had changed AV programs. Sure enough ...

Darn, it's Kaspersky! Turned it off and downloading now. What good is an AV if one has to turn it off to do anything, geez. As soon as the downloads started, I turned the AV back on and they continued fine.

Thank you all for your patience, I have no idea why Kaspersky was blocking the server for some but not all downloads.

Downloads just completed :-)