cron give error 500

I’m quiet noob with drupal. I have a cron with an error. The show error :

Fatal error: notifications_cron_queue_event_worker(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Notifications_Node_Update_Event" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide an autoloader to load the class definition in /var/www/scougralap/www/sites/all/modules/notifications/notifications.module on line 1434 

The PHP version is 7.2, it could be the problem ?