Hey Josh, thanks for getting back. I did deactivate all plugins (except for the events calendar and ical importer) and switch to the 2014 theme before posting.
Just now, I switched to the 2013 theme and cleared cache, per your suggestion. After doing so, I got the “Your search had no results” error.
I then activated the plugin Optimize Database after Deleting Revisions to clear out deleted event data, as was suggested on another thread (https://theeventscalendar.com/support/forums/topic/can-not-import-events-again-after-deleting-them/), and then re-ran one-time import/search with a start date 11/1, which resulted in 15 events. Far less than the number in the ics file.