This bug affects teachers who have the same students in multiple courses. If a student exists in a group in one course the teacher teaches, but does not have a group set in another course taught by the same teacher, that student's submissions will not show up for grading in the course without a group assignment.

To reproduce this bug, please follow these steps:

1. Create two courses (Course 1, Course 2)
2. Create four users (Teacher, Student 1, Student 2, Student 3)
3. Enroll Teacher in the Teacher role in both courses
4. Enroll all three students in the student role in both courses.
5. In Course 1:
a. Create a group (Group 1)
b. Add Student 1 and Student 2 to Group 1
6. In Course 2:
a. Create a group (Group 2)
b. Add Student 1 to Group 2
c. Create an Online Text assignment (Exam 1)
d. Log in as each student and submit Exam 1
5. Log in as the teacher and add the AJAX Marking block to a page

If all steps have been followed correctly, you should see submissions for Student 1 and Student 3, but not Student 2.

Student 1 shows up because they exist in both groups
Student 3 shows up because they exist in neither group
Student 2 does not show up because they exist in a group in Course 1 but not in Course 2.

This bug seems to be related to the way that the group tables are joined in the fetching query for submissions.