The Webmin Actions Log is useful for debugging and for applying fixes (e.g., rollbacks) if something goes wrong. However, it's not complete when Virtualmin GPL is in use.
E.g., when a Let's Encrypt certificate is installed, commands up to the point when the certificate is downloaded are not logged.
E.g., when Virtualmin : Re-Check Configuration configuration is done, commands used to obtain system information, e.g., amount of RAM, version(s) of installed PHP, are not logged.
E.g., when Webmin : BIND DNS Server : Apply Configuration is done, the command(s) used are not logged.
A more complete Actions Log would be even more useful.