Your PHP version is out of date, but as I alluded to earlier updating this requires you update all the php extensions to the correct version too.
Do you see anything in your PHP error log (/var/log/apache2/error.log)?
What happens if you disable the cron job and manually run the command (comment out the parser line in /etc/cron.d/itflow and then manually run sudo -u www-data php /var/www/support.<yourdomain>/scripts/cron_ticket_email_parser.php, potentially a few times before the lock is removed)?
