I have come across this unusual issue in SharePoint 2013. I have requirement to search file server for which I created a content source and ran full crawl.
All crawls were successful and verified from crawl log also. After this I created Result source and through Query builder tool specified the content source as Newly created Content Source and ran the query here also I got the desired results.
But after modifying the search result web part through query builder tool and running the same query as was in result source the query resulted in 0 results. What am I missing?