Testing an upgrade from 5.13.4 to 5.17.4 on wordpress, I get a fatal error. This is on PHP 7.1.32.
PHP Fatal error: Uncaught Error: [] operator not supported for strings in /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Upgrade/Incremental/SmartGroups.php:105
Stack trace:
#0 /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Upgrade/Incremental/SmartGroups.php(48): CRM_Upgrade_Incremental_SmartGroups->datePickerConversion(Array)
#1 /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Upgrade/Incremental/Base.php(233): CRM_Upgrade_Incremental_SmartGroups->updateGroups(Array)
#2 /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Queue/Task.php(88): CRM_Upgrade_Incremental_Base::updateSmartGroups(Object(CRM_Queue_TaskContext), Array)
#3 /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Queue/Runner.php(217): CRM_Queue_Task->run(Object(CRM_Queue_TaskContext))
#4 /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Queue/Page/AJAX.php(52): CRM_Queue_Runner->runNext(true)
#5 /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Queue/ in /home/dhwpuser/testdomain/wp-content/plugins/civicrm/civicrm/CRM/Upgrade/Incremental/SmartGroups.php on line 105
This appears to be a well known issue with PHP 7.1. See for example this issue.
SELECT id, form_values FROM civicrm_saved_search WHERE LEFT(form_values,1) <> 'a';
. If any results come up then that might be the culprit - compare the id field to the group ids you have listed on the manage groups page in Civi. EDIT: I see recent versions of civi don't show the id anymore on that page. Hover over the Settings link on the right and look at the id= part in the url and that's the id. – Demerit Sep 20 '19 at 2:30