I see that behavior when I Delete a user rather than just setting the user Inactive. (I had to refresh the browser page on the policy to see the Unknown User bit).
All I can think of is to go into the People settings and show just Deleted users. If allowed by your organization, you can restore the deleted users, then set them Inactive, and that should restore their names to the Policies (if that's what you really want).
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George Ganahl GCP (Genesys Cloud), CCXP
Principal PS Consultant
Genesys
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