Often instructors have to give the class a little more time to complete a quiz, like if there has been a campus emergency and instructors need to extend the (say) 24 hour period that students have to complete the quiz. 

A new instructor will think that the best way to do this is to edit the due date on the assignment page. However, quizzes that are in progress will automatically submit at the original due date. Other students who start the quiz after that will be able to use the later due date. This is very difficult behavior to track in canvas for novice instructors.

Please modify the warning about changing the due date for in-progress quizzes and assignments to say that the best option is to add time to the students using quiz moderation, and actually walk them through that process. A due date should not be changed while an assignment is in progress.