When moving between student quiz submissions in SpeedGrader (using the left and right arrows at the top), the numerical scores are saved, but the "additional comments" fields below the questions are lost. In order to save these comments, you must click "Update Scores" before switching to another student's submission. (This is all using the "Grade by question (beta)" option -- not sure if that makes a difference.)
I've been told by Canvas Support that this behavior is intentional, but my request is that the "additional comments" fields below the questions be saved, like the numerical scores are, when switching between students, even without clicking the "Update Scores" button. It is quite natural to simply switch to another student when you are done with one, but that simple action erases (potentially) a lot of work commenting on the first student's quiz.
Also, clicking "update scores" and waiting for the refresh takes a long time. And then you still need to click to the next student and wait for another screen refresh. It would be great if the comments were automatically saved.