MID Server "Validated" field keeps stuck in a "Validating" state.
This might occur especially after an upgrade or install.
London and newer releases
This occurs when the time/date set on the MID Server server is not sync'd or it's different from the Time Zone configured on the same server.
Example: The MID Server is running in a Windows Server with a Time Zone configured to Amsterdam Time Zone. However, the actual time/date is not sync'd or is different.
Make sure the time and date are correctly configured to the Server time zone.