Are you referring to "restricted" incidents? In a recent update (I believe 6.2) the option for the admin account to view all incidents that are also marked as "restricted" was removed. From my understanding, if the incident is marked as "restricted" and the admin account is not an explicit team member of the incident, then the search will not return the restricted incidents.
You could use something such as Team Management Pack to add the admin account to each incident that is restricted.
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