When you create a batch job by default the job is executed by the user who created it.
If for some reason the user is disabled by a system administrator (for example because he leaves the company where he works) the jobs stop executing and disappear from the jobs form.
In these cases to preserve the execution of the jobs you can modify the execution user by changing the “Run by” field.
It is a best practice to use an administrator account or a service account.
So let’s change it (as shown below)
Go to > System administrator > batch jobs
Access the jobs, click on Edit and change the “Run by” user.