The Reported Date property in the versions ePO 5.10 listed above, were designed originally to use a combination of both:

• Product Properties
  And
• Most crucially for this issue, Product Deployment or Installation Event Data.

A null or blank value is displayed if there is no Product or Installation Event Data associated with the managed endpoint for the Reported Date column. A blank or null value is displayed despite the product being managed, and reporting all other product properties successfully 

The following are the reasons why the 'Reported Date' column displays a null or blank value:

• Events are disabled.
• System was deleted, and readded, post a product deployment.