cPanel updates fail to stage new RPMs with a "No digest data for $RPM" error

Symptoms

Nightly cPanel updates fail with an error indicating an inability to stage a new RPM due to missing digest data. For example

[2021-08-3 11:32:04 +0100] ***** FATAL: Failed to stage “new RPMS” because of an error: No digest data for cpanel-libspf2-1.2.10-2.cp1198.x86_64.rpm at /usr/local/cpanel/scripts/updatenow.static-cpanelsync line 51552.

Description 

This can indicate an issue with a FastUpdate or otherwise custom update mirror specified in /etc/cpsources.conf.

Workaround

Comment out the HTTUPDATE= line(s) in /etc/cpsources.conf, and try the cPanel update again. Lines can be commented out by placing a '#' in front of them. For example:

# HTTPUPDATE=203.0.113.5

A manual cPanel update can then be run with:

/scripts/upcp