Doug - Can you take another look at the [coursename]_set_user table in the database. You wrote:
The one difference I noticed with the student in question was the 'lis_source_did' column of the [coursename]_set_user table was NULL. For the other students, it was populated with a long hexadecimal-looking string.
- Does this student have non-NULL values for 'lis_source_did' for other assignments?
- Are there any other NULL values for 'lis_source_did' in the table and if so is there any noticeable pattern?
Could you also confirm that this student was able to do prior assignments when the LTI grade passback was enabled.