We use this feature all over the web app including this site collection where the lists/libraries seem to have stopped returning results. All other libraries in other site collections still working fine.
Only thing that has (knowingly) changed is that I created a new site page and added search web parts so that this site could be searched in isolation without results from outside the site collection. I use the same result source as the global search with the other differences being that I send the results to a web part on the same page as the search box and I also added a property filter to restrict results -
Other than this the site collection is as it has always been. Have I inadvertently done something to break "find an item" when I set up this new search page?