I had the problem come up again briefly, but a reboot cured it. FWIW, it only happened on my iMac with multiple users logged in, but not on my MB Air with only me logged in. Also, the iMac is "descended" from a PowerMac 7600 running MacOS X beta and 10.1 via ExPostFacto which had my accumulated data from Systems 7, 8, and 9. That was superseded by a PowerMac G5, which was replaced by a 2010 iMac, which gave way to my current 2018 iMac. Each new machine inherited the prior one's configuration and data via Migration Assistant or whatever. So, there's a lot of cruft there and that may explain some issues, but I still find myself looking for old emails and stuff from way back now and then so a clean install is out of the question. Pretty amazing that things still work.
When it occurred originally, I was getting one result from a search that I knew should have many more. Now that it appears to be fixed, I seem to be getting everything, but I don't have complete confidence since this thread keeps going on with people having issues.