"Overdue Today" in the Lender work queue shows requests that are Shipped and the due date has been reached (so they have not yet been actioned Overdue, but are ready to be). It does not show requests that have actually been actioned Overdue; these are found in the "Overdue > 4 weeks" section of the work queue, but only if the date of the overdue action is 4 weeks old or more.
Newly Overdue requests can be retrieved using the Advanced Search by selecting:
Your Library's Role = Lender
Status = Overdue