by Daniel Tran.
Hi Mary,
Unoconv appears to work now.
I did not change anything on the system side. (RHEL 6.x, PHP 7, Moodle 3.1)
After reading this tracker: https://tracker.moodle.org/browse/MDL-54554 , in there Howard mentioned "My observation is that once Moodle has tried to convert the document it doesn't try again. So, when testing this, if a document conversion fails you have to upload a new one before trying again. I couldn't find anyway to 'reset' this (which would be handy)"
I decided to remove the submitted assignment and resubmit it. It worked.