The reason why there are no results for thos items is because they are not stored as attachments, but as a custom post type 'um_docs': https://i.imgur.com/dS1vHen.png
When I selected that post type, searching for 'XYZCBS' yielded the result as it shoud. Content of the documents are however not searchable, and very possibly it won't be possible in the near future. There is something in development, but there are many issues regarding indexing .pdf files correctly.
One other problem is that the post type URL for the downloads appears to be returned incorrectly, so WordPress returns an URL to a page which does not seem to be exist. I've added the following custom code to the bottom of the functions.php file in your theme directory to resolve that:
I will leave it here for future reference.Best,
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