If your search is no longer working after an upgrade from 3.1.17 to 3.2.2 or above, make sure to set search relevance to false. 

In the faqconfig table, set search.enableRelevance to false.

Or in the GUI, here:

If you can't save any settings in the GUI, clear your site cookies and log back in. Also ensure any caching systems aren't caching /admin.