Disappearing Assignment Submission (2.6)

Hi All - 

Running Moodle 2.6.  

A student submitted an assignment as an attachment - report logs confirm a file was attached. Submission went through - shows on the grading page with a time stamp and says "submitted." But the file is gone. 

Any ideas why? Any chance it can be retrieved?  So far this is a one-time, isolated incident.

Thanks,

Erin