I recently worked on an issue where Excel files on File share were getting crawled just fine. However if you search on their filename you will see the result pulled up however the Filename is blank in the search result.
Note: this happens for fie which have their metadata "title" with no value. i.e Within the file if we go to file->prepare->Properties. Keep the title value empty.
Two workaround that I found are:
1. Manually add value to the title field of the file and then run a crawl
2. Put basic:10 at top of mapping to MP “title” and then run full crawl
The fix is now a part of the July CU also mentioned in the KB:
When you crawl a file (.xlsx or .xlsm) that is created by Microsoft Excel 2007 or a later version of Excel on a file share, the file name appears in blank on the search result page.
The link for downloading the CU is https://support.microsoft.com/en-us/kb/3054937