Search not working in specific sites

Global search is not working on root install and newer sites.

We have verified that post indexer IS indexing the sites in question and it is the latest version of the plugin. We've gone ahead and "rebuilt" the index just in case. We removed and reinstalled the search plugin but it still will not function on the root install, and newer created sites.

Current migrated version of the site is now on WPEngine and is only viewable/accessible with a hosts file switch. Live version of site displays the same issue for the newer sites but the root site's global search works fine on the live but not on the migrated. So one additional change between migrated and live.

Ideas on how we can troubleshoot?