I'm getting the following message about 3 or 4 times a day from cron. Nothing is showing up in the error log and I'm puzzled. This follows moving the site from one host to another which must be a clue. Civi is working fine except for this error message. The site is Drupal based, release 5.19.4 and PHP 7.3.15. After putting in the line suggested by Demerit, here's the new trace, the problem occurred once today.
Warning: array_intersect_assoc(): Expected parameter 1 to be an array, string given in /home/example/public_html/sites/all/modules/civicrm/Civi/Core/SettingsMetadata.php on line 150
Warning: array_intersect_assoc(): Expected parameter 1 to be an array, string given in /home/example/public_html/sites/all/modules/civicrm/Civi/Core/SettingsMetadata.php on line 150
Warning: array_intersect_assoc(): Expected parameter 1 to be an array, string given in /home/example/public_html/sites/all/modules/civicrm/Civi/Core/SettingsMetadata.php on line 150
Warning: array_intersect_assoc(): Expected parameter 1 to be an array, string given in /home/example/public_html/sites/all/modules/civicrm/Civi/Core/SettingsMetadata.php on line 150
Warning: session_start(): Cannot start session when headers already sent in /home/example/public_html/sites/all/modules/civicrm/CRM/Core/Session.php on line 124
And here what was in ConfigAndLog at the time the problem occurred
Mar 18 02:15:02 [info] ddd DD
Mar 18 02:15:02 [info] month
Mar 18 02:15:02 [info] 500
Mar 18 02:15:02 [info] en_GB
Mar 18 02:15:02 [warning] Deprecated Path: There is a setting (generate_schema_and_data) not correctly defined. You may see unpredictability due to this. CRM_Core_Setting::setItems Array ( [civi.tag] => deprecated )
Mar 18 02:15:04 [warning] Deprecated Path: There is a setting (generate_schema_and_data) not correctly defined. You may see unpredictability due to this. CRM_Core_Setting::setItems Array ( [civi.tag] => deprecated )
if (is_string($fieldValues)) { CRM_Core_Error::debug_log_message($fieldValues); }
and then that should at least give a clue in ConfigAndLog as to what.