The “Last logon” field within AD Janitor is not accurately presenting the users logon timestamp.
The ”Last logon” field/attribute belongs to the type of AD information that isn’t replicated between domain controllers.
“Last logon” depends on what DC the client is communicating with during the logon. It will be different on all domain controllers and the account creation attribute will only be visible on the DC that was contacted during the creation of the user account.
If you in Specops AD Janitor go to Scan properties, “all the DC’s” and tick “Last DC” then the latest “Last logon” that is found on a DC will be displayed.