by Emma Richardson.
Yes, once submissions have been made, it throws the database into total disarray especially if you move a student who has already submitted. If they are set to one assignment per group, how does Moodle know if the assignment follows the student or stays in the group.
I think we need a tracker item to somehow lock this down and not allow changes to be made that can this affect but it would not be easy as groups and groupings apply to a multitude of things.
I would suggest, recreating the assignment from scrap and making sure that the grouping is set up correctly before allowing students to submit.
You could try going to View/Grade All Submissions and deleting the offending entry from there - that might fix it.