Action Owner LOV - inconsistent behavior

Summary

Action Owner LOV does not populate with User Names and the behavior is inconsistent

Content

EHS Manager logs and Incident.  Trying to Add Action for the Incident.

Relevant details entered in Action Details section fields. 

Navigate to Action Owners section.

The Action Owners LOV is defaulted with the logged in user's name. User wants to enter other user to designate as Action Owner.
However on clicking in the Action Owner LOV to select other other user the LOV does not show ANY name and keeps spinning. ( screenshot)

The behavior changes if after entering the Action Details one clicks Save ( NOT Save and Close).