Registry entries for group policy settings can potentially be changed from the required configuration. This could occur as part of troubleshooting or by a malicious process on a compromised system. Enabling this setting and then selecting the "Process even if the Group Policy objects have not changed" option ensures the policies will be reprocessed even if none have been changed. This way, any unauthorized changes are forced to match the domain-based group policy settings again.
To fix this configure the policy value for Computer Configuration >> Administrative Templates >> System >> Group Policy >> "Configure registry policy processing" to "Enabled" with the option "Process even if the Group Policy objects have not changed" selected.
STIG: Server 2019: https://www.stigviewer.com/stig/windows_server_2019/2020-06-15/finding/V-93251