If you navigate away from a SpeedGrader page before submitting your comment(s), Canvas generates a message warning that you have unsaved comments on the page.
Note: This feature only applies to leaving the SpeedGrader page; it does not apply to the comment field for each student submission. If you create a comment for a student but do not submit it before viewing another student submission, SpeedGrader retains the comment in the comment field for the second student—and any student—until the Submit Comment button is clicked and the comment is officially submitted as part of a student’s submission.