A user may not be able to see the Customers with past due invoices if the Finance Charge Preference does not contain a value for Grace Period.
Navigate to Setup > Accounting > Finance Charge Preferences
Make sure that Grace Period has value on it
If none, set a value for the Grace period field (Ex. 0)
Navigate back to Transactions > Customers > Assess Finance Charges page
Note: Customers with past due invoices will now show up