- Student can view "Preview" in Submission Details because it's rendering in Crocodoc viewer. After teacher grades the assignment in LTI, it won't display because it was edited in Feedback Studio.
-- I believe dreesd reported a similar issue to support, but, in his case, I think his instructors wanted to grade in Crocodoc. To me, it makes sense that if the grading occurs in Tutnitin that students would not need or want to access Crocodoc as the original file, originality report, and instructor feedback would be available on the Turnitin side. Perhaps I am misunderstanding the need for Crocodoc?
I don't think my students ever look in their files area at all, but I direct them to Turnitin if they would like to download the original file as submitted to the assignment. You could file a ticket with Canvas support and see what they say on this issue. Perhaps it is a bug because the idea is that Turnitin sends a copy of the file back to Canvas, so it makes sense that the file would be connected to the student's materials in Canvas.
- Differentiated assignments - if there is an "Until date" and "Due Date" set in Canvas for a student, they will see the due date and until date on the assignment details page. If the "Until Date" is removed, the student's due date is now the other student's due date.
To the best of my knowledge problems with differentiated assignments is a known shortcoming / design issue of external submission assignments. Canvas has differentiated assignments, but Turnitin (and many other external tools) do not. The known work around is to only differentiate one group of students and to add a separate assignment for each group needing a due date. There are more details on working around this problem in the blog Chris referred you to. Hopefully, I have understood your need here.
I hope that helps!
