I have been grading for the past 4 hours using speed grader. I was down to almost the last 2 or 3 assignments when one student submitted a file with a HEIC extension example img-oo12.HEIC (I could not open this one) and when I finished entering her comments plus score, and I tried to move forward on the speed grader, it did not move. So I did a download submissions I think and everyone's assignment plus grades disappeared leaving me with only one submission. 

Does Canvas save previously graded assignments with scores? I hope the answer is "yes". I tried closing all browsers and reopening them, but I have lost everyone's assignment except one student's with the HEIC extension. 

Please get back to me regarding this at your earliest convenience. i am now really skeptical about speed grader.