Considering Pantheon Files ("File Manager" in Loki, not to be confused with Nautilus sometimes called "Files") the search tool it's a bit different and rather limited compared to those of Nautilus or Dolphin, or to specialized tools like Catfish or Gnome-Search - especially in the way it displays the results.
Typing or clicking during search process will stop the search. Take care not to type or click during search process. More here.
The results are listed just as a drop-down list (and not as a file manager window or search-tool window) that also never contains more than ten items and that goes away in a second if you click or focus away in any way. (So, the search is 'recursive' with Ctrl-F but you only get ten results).