I decided to try out Energy Saver, and checked by default is "Pause non-essential processes", which includes Spotlight. I have absolutely no idea what the conditions are to trigger it, but I discovered that Spotlight was completely disabled at some point recently, and the only change I had made to my system configuration was to enable Energy Saver. As part of a diagnostic with Microsoft to figure out why Outlook wasn't allowing me to search my email, I ran "sudo mdutil -E /" and this was the output: kevindean@Kevins-MBP ~ % sudo mdutil -E / /: 2019-11-23 14:58:02.922 mdutil[15170:594655] mdutil disabling Spotlight: / -> kMDConfigSearchLevelFSSearchOnly Indexing disabled. Once I figured out how to re-enable indexing, the search problems I was having went away. I obviously can't be sure that Energy Saver was the culprit, but it was the only logical choice. Honestly, all I have time for is to submit this thread; I don't have time for diagnostics, as Energy Saver isn't important enough for me to invest any more time in.