In our case we have an assign using Marking Workflow, blind marking and group submissions. As a teacher, I set a grade to a certain user in the app, but I don't add a comment or anything else. After that, in the app I cannot know which grade the user has because the WebService mod_assign_get_submission_status doesn't return the feedback (the feedback includes the grade).

I looked at the code and I've seen that get_assign_feedback_status_renderable only returns the feedback if:

$hasgrade || !$emptyplugins

$emptyplugins is true because as a teacher I didn't fill any plugin (the grade doesn't count as a plugin). And $hasgrade is false because the instance has a grade but there is no gradebook grade (because of Marking Workflow). IMO the feedback should be returned in this case took, otherwise the app cannot know the grade of the user.

How to reproduce:

1. Create a course using groups and Marking Workflow.
2. Create at least 2 groups in the course.
3. Enrol at least 2 students in the course and a teacher.
4. Add the users to the groups.
5. Restore the assignment attached to this issue in the course.
6. As a teacher, login in that site using the Moodle app.
7. Open the assign in the app.
8. Open any student and add a grade but not a comment.
9. After the grade is sent, open the student again. Check that the grade field is still empty.