This discusses the reasoning behind some potential unexpected behavior regarding searches in the Reports module. The search box utility lets you search 'all' reports, but there may be instances where the expected reports do not appear in the search results.
It can cause confusion because if the same user searches directly on the [sys_report] table, the result is returned.
Release or Environment
Madrid, New York
This is usually due to Report Share Settings. If an end user only creates a report and maintains the visible setting only to 'me' then other users will not be able to see that report in the Reports UI. This doesn't stop admins or other users with sufficient permissions to search/find the report on the [sys_report] table directly.
This is expected behavior. It is recommended to review the Share Settings of that report by contacting/impersonating the affected user.
Please see the documentation here for Report Share settings.