Job not running on Schedule
Commentary on this question:  Looking over this post I observe that your job was originally running as 'sa'.  It appears that the service account for your SQL Server was not given rights to the necessary file shares.

This is apparently what led to the job looking as if it were "Running" forever. Of course, nothing was actually happening.

It is a best practice to withhold giving the SQL Server service account rights to any non-essential folders. This helps keep the SQL Server environment from being exploited for unsafe activities.  (Much the same reason that the xp_cmdshell stored procedure is disabled by default.)

When you switched from sa to an account that had the needed rights to the file system everything worked.  Which was, of course, the right thing to do.

Scheduled SQL Agent jobs do sometimes hang (but look like they are still 'running') for a long time. Likely this is usually due to external issues, such as not getting access to file system. 

As long as the SQL Agent believes the job is "running", it will not try to start the job again.

Simple lessons:


Think of 'sa' as ruling the SQL Server, but must beg for rights elsewhere.
When reviewing SQL Agent job history, be alert to jobs that have been running much too long. That usually means that the SQL Agent does not realize that the process has died.
Always plan to use a proxy account for SQL Agent jobs that need to access data or objects outside of the SQL Server. And make sure that the rights are granted to the Credential that the Proxy is using.


And, of course, every rule has exceptions.