I recently altered the due date for an assignment to allow several students to complete it. I then marked all of the assignments. I checked the calendar to make sure that the next due date was correct and saw the altered due date on the calendar. I didn't want the rest of the students to think they had an extra, unexpected assignment due the next week so I clicked on the assignment IN THE CALENDAR to delete it from the calendar and Canvas deleted the assignment (with all of the marks and comments for each student) FROM THE COURSE! There was no record of the assignment anywhere in the course nor of the grades. Luckily, when I contacted the "help chat line", the individual was able to restore the assignment to the course.
I am a sessional online instructor and only teach one course per year, like many of the online instructors at the colleges in this province. PLEASE, include a pop-up warning when an instructor goes to delete an assignment from the calendar to let that instructor know that if they delete the assignment from the calendar, it will also be deleted from the entire course!