FLUSH CACHE has caused WHITE SCREEN

I merely did a Drupal "Flush All Caches" from the main admin menu. I can no longer access the site. In the HTTP error log I get: [Thu Jul 11 11:48:34.537141 2019] [php7:error] [pid 5699] [client 157.55.39.212:11042] PHP Fatal error: Declaration of RulesConditionalEmptyUI::form(&$form, &$form_state, $options = Array) must be compatible with RulesContainerPluginUI::form(&$form, &$form_state, $options = Array, $iterator = NULL) in /home/scvoa/domains/courses.socalvoa.org/public_html/profiles/opigno_lms/modules/contrib/rules_conditional/includes/rules_conditional.ui.inc on line 39 This is an active production site that is in the middle of testing. My most recent backup is 3 weeks ago. If I must go to the backup many people will have to retake tests. PLEASE LET ME KNOW HOW TO RESOLVE THIS. URGENT! Are there only certain tables that I can recover from backup that will fix this error and still keep test scores?