Currently, if you opt out of notifications for student assignment submissions, you will also not receive notifications when students submit comments in assignments.
This needs to be separated. Assignment comments are like emails and it's important that instructors are alerted when these comments are submitted. But it's annoying to be notified every time a student actually submits an assignment.
Therefore, please separate these two notification settings so that instructors can receive the assignment comment notifications, but not the assignment submission notifications.