What causes iCloud library update errors on Mac?

I continue to get this message: "There was a temporary problem completing your request. An unknown error occurred (11571)."

I have signed out and in to my account. I have upgraded to Sequoia 15.5. I have restarted the router. I have restarted the Mac Mini M4. I can't access the Music Home. I have checked for an outage on the Apple website.

When I select "update the cloud library", I get an error message to try again later. I've waited and tried again over a few days.

I am flummoxed.

[Re-Titled by Moderator]