No Output from Cron

I recently replaced my USB backup drive.  I partitioned and formatted 
it, and when I ran my backup cron job (The relevant commands are 
/usr/bin/rdiff-backup -v 3 /var /backup/rdiff/var and so forth) I got 
the error message that it could not create the target directory 
/backup/backup/rdiff/tar. (/backup is the target mount point.)

I created /backup/backup, and now the only output I get is the messages 
from mounting the drive (successfully).  No files were created.

I increased verbosity to 9, but got no additional output.

The cron job used to deliver the "echo" output from the bash commands, 
but never did return any messages from rdiff.  Now the only messages are 
in the syslog from the "mount" command.

Running the job manually, I did get output in /backup/backup/rdiff/var, 
but the job was interrupted.

This is a legacy configuration that was originally built on Debian Etch 
and is running on Stretch.  rdiff-backup is version 1.2.8

Jonathan