When more than one language is configured in Intelligent Search, the Explain Search won't return any results if matching with an admin locale which is also in Intelligent Search, but it's not the exact match. For example:

• Languages in Intelligent Search: es-AR and en-US
• Selecting es-AR in Explained Search and the admin locale is en-US; no results are shown.

• Access the Explain Search and select a language;
• Select a language in the admin that is also in Intelligent Seach.

Select the exact language in the admin or any that is not configured in Intelligent Search.