I still didn’t test that but I think that the issue is the following:
Cerber is making a call to a function that doesn’t exist in WP version 4.43 “wp_authenticate_email_password()”.
AH01071: Got error ‘PHP message: PHP Fatal error: Call to undefined function wp_authenticate_email_password() in /var/www/vhosts/macgregorschoolwear.co.uk/httpdocs/wp-content/plugins/wp-cerber/cerber-load.php on line 953\n’
I think that installation of the older version of Cerber should fix this or upgrading WP.