Moving caps.json from the plugins folder seems to reset the Power Search settings. It's re-indexing all the files.
I accidentally deleted the ES data folder when I reinstalled ElasticSearch (I use Geek Uninstaller) but since the caps.json file listed the files as already-indexed, it didn't re-index them.
Another possible bug I noticed: When canceling partway through indexing (e.g. to adjust the number of threads), although the files are indexed (as can be confirmed by monitoring the elasticsearch programdata folder), the datetimes don't get added to caps.json so Power Search ends up re-indexing them unnecessarily.