I installed Turnitin's Moodle Direct plugin in June, but only this semester have I had instructors really start to use it. I currently have Moodle 2.4.5 installed on the server. Things have mostly gone okay, but the two instructors who use it the most have had issues with some of their students' assignments missing. They appear in the submission inbox as assignments that haven't been submitted to Turnitin. When instructors try to click on the assignment, there is no download, and when instructors click the "Submit to Turnitin" link, the Moodle Direct plugin fails to send it to Turnitin.
After a little troubleshooting, I have found that although the file appears to exist in the submission inbox (and in the "turnitintool_submissions" table in the database), the file doesn't actually exist on the server.
Has anyone else had this problem or might know what would cause it? I've had lots of contact with Turnitin support; however, the cause of the problem hasn't been resolved.