Before we dig any further in to any issues raised, the first thing to do, before we try anything else, is to see if your hosting (WP Engine) is the issue (this may be the issue, as the symptoms you describe is what this causes).

There is a setting to override a ‘feature’ of WP Engine hosting, that truncates long SQL queries (which ours are). Edit the site wp-config.php file and add this at the top, after line 1 (on a new line 2):

define('WPE_GOVERNOR', false);

PLEASE DO NOT COPY code from the email you receive for this reply, as email systems sometimes alter the quote marks and encode some characters; instead copy it from the actual forum page.

(also see here for another related support note about this – https://support.searchandfilter.com/forums/topic/killed-query-errors-in-log/#post-64826)

It looks like you have some custom JavaScript on that field?

I will leave the thread open for you to reply in, or let me know it is sorted. It looks to me that some javascript is intercepting the click/change event, so S&F doesn’t see it.