When running the queue worker with on a Laravel Notification that returns a mail and a database entry it causes a crash, because of the function getJobId that expects a string but returns a int.
What Laravel version and queue driver are you using? Illuminate\Contracts\Queue\Job::getJobId() has returned a string since Laravel 6.x. I assume 5.6 and 5.7 also returned a string.
When running the queue worker with on a Laravel Notification that returns a mail and a database entry it causes a crash, because of the function getJobId that expects a string but returns a int.