Steps to reproduce:
Login as super-admin user.
Choose a problem and acknowledge it.
Find System status widget with a problem.
Find this problem in widget, open popup overlay and hover on Yes.

Result:
User in popup: Inaccessible user. (See screenshots)

Expected Result: Super-admin should see himself as Admin (Zabbix Administrator).

On other pages like Event acknowledgement form, Problems page, Problems widget in other similar popups user appears correctly.