Oh, I believe the error is with regard to it being placed in maintenance mode.
? ? public function check_if_maintenance() {
? ? ? ? if ( ! is_admin() && ! $this->is_wplogin() ) {
? ? ? ? ? ? $maintenance_mode = (bool) get_tutor_option( 'enable_tutor_maintenance_mode' );
? ? ? ? ? ? if ( false === $maintenance_mode || current_user_can( 'administrator' ) ) {
? ? ? ? ? ? ? ? return;
? ? ? ? ? ? }
104----> ?? header( 'Retry-After: 600' );
? ? ? ? ? ? include tutor()->path . 'views/maintenance.php';
? ? ? ? ? ? die();
? ? ? ? }
? ? }