Software Sources hangs and crashes if 1 server is offline

The Darktable repository is currently offline:

This causes the app Software Sources to “Refresh Software Cache” for minutes, only to report an error, after you send the report, it is still loading and you have to force close the loading screen and Software Sources.

Running sudo apt update clearly shows that one repository is offline.

Software Sources should not hang indefinitely when a server is offline right?
This is on 20.10.

Correct. It should be able to cope.

Suggest file a bug report on launchpad

Sorry bad behaviour to report an obvious Ubuntu bug here first.
I have filed a bug:

no - no - more than happy to discuss further here - then direct to the most appropriate place as part of that discussion.

BTW - that bug link appears to be invalid.