As an admin when you search for Item or any users, only few users show up that belong to a certain domain.
Though the admin does not have any domain restrictions the results returned are of only certain domains.
Learning Management System
The most probable cause of the issue is that the admin has added only certain domains in the Viewable Domains.
Viewable Domains are a type of search filter, and in some cases a filter when generating reports. It works like a filter on the Domain criteria of searches.
For example, if you have access to domains 1-10, but you usually work with only domains 1-5, they you can set your user viewable domains to domains show only domains 1-5.
To add domains to the filter, click Edit and then add the domains that you want to view.
In case you would wish to have the admin access all the domains then just remove all the domains from the Viewable Domains.
Domains not visible, Search does not return all items, Search does not return all users, Search does not return all domains , KBA , LOD-SF-LMS , SuccessFactors Learning , LOD-SF-LMS-COR , LMS Core - Items, Catalog, Curricula , Problem