It claims to have "Applications" selected on the right side, but doesn't find anything other than Files & Folders. I have no way of launching programs except via terminal. And no way of finding the list of installed programs.
I tried removing the zeitgeist index as per this similar question, but it didn't do anything.
This is what I see when I open it:
More info: I've been having this issue for months on 16.04, and hoped it would be fixed by upgrading to 18.04. It was, of course, since that switched me to GNOME Shell 3, but I switched back to Unity so I could get all of my custom compiz settings, and the issue came back.
More more info: none of the toggles on the right seem to do anything, except the Files & Folders one, which, if unselected, means that nothing gets shown as results.