What does NO DATA AVAILABLE mean in the User and Role Access Audit report?

Summary:

We are required to run the User and Role Access Audit every quarter and there are users who appear on the report with 'NO DATA AVAILABLE' in the Policy Stripe, Assigned Role Name, Assigned Role Display Name and Assigned Role Description columns.

We have many Not Managed by HR users in our system, but only a small number appear on the report. Not Managed by HR users should not have any assigned roles, so we are unclear as to why these users are appearing on the report despite not having any roles and why not all other Not Managed by HR users are on the report since they are no different from the small group that does appear.