I am getting that sane error on PHP 7.0, and it must be recent. It happens running the cron, and until a few days ago that was working perfectly.
PHP Fatal error: Uncaught Error: Non-static method Misc::currentURL() cannot be called statically in /home/netthost/domains/ost/osticket/bootstrap.php:369
Stack trace:
#0 /home/netthost/domains/ost/osticket/main.inc.php(23): require()
#1 /home/netthost/domains/ost/osticket/api/api.inc.php(26): require_once('...')
#2 /home/netthost/domains/ost/osticket/api/cron.php(17): require('...')
#3 {main}
thrown in /home/netthost/domains/ost/osticket/bootstrap.php on line 369