Hi Josh & Todd,
This is caused by the events queue that is processed by the cron being stuck. If an event being processed returns false then Moodle's cron doesn't process any more events of that type, therefore if 1 submission fails no more will be sent to Turnitin until that event is correctly processed.
We have seen a few people with the same issue and in all cases so far the problem has either been with the assignment itself or with a user on the Moodle side being setup incorrectly. When submitting to Turnitin the plugin will create the class and user - if necessary - then create/update the assignment, if one of these fails then the submission can not come through to Turnitin, which is what causes the events queue to be stuck.
We are working on improving this so that all events are processed including submissions where there are non-submission related issues but failed submissions are added to the plugin's errors page along with submissions which fail for normal reasons.
Can you enable diagnostics in the Turnitin Assignment 2 section of site administration and check the API and Activity logs after the cron has run and see if there are any errors returned by the Turnitin API? You could also enable full Moodle debugging and check the cron output to see if an error has been output.
Let me know if you get anywhere. If not, I'd point you towards Turnitin product support and we'll take it from there.
Regards
John
by John McGettrick.