This behavior has been intermittent over the last few years (now the latest kde 5.5 from the ubuntu xenial repos). Open krunner, type in a file name. The file doesn't show up in documents (usually--sometimes it will show up in recents). Strangely, it seems confined to xls/xlsx/doc/docx files. If I type in "xls", no docs show up. "ods" works as expected. Same thing with "doc" v. "odt". I've tried a few suggestions about resetting the baloo database without success. From dolphin, search also works correctly. So it appears the files are being indexed correctly, but for some reason krunner isn't doing something right...

I can confirm that KDE Application Launcher doesn't find any xlsx or docx files. Doc-files however are found.

I experience the same issue on the latest KDE Neon. Do you know where exactly we can write this Issue, is there a Krunner web-site?