My students take timed assessments in Quizzes next. I have them submit a picture of their scrap paper in the comments after the timer runs out. Some students get an error message saying they are not authorized to submit in the comments. Other students are able to upload files just fine. I have tried telling them to use the chrome or safari web browsers and to not use the canvas app. Some try everything and it doesn't work. Is there a way I can change the settings in the quizzes next to allow the students to submit comments no matter what format or system they are using?
The most likely explanation is that the students with problems are using a browser that saves cached pages to speed up web browsing. The cached page of the assignment page would still look like no submission had happened even after the quiz was submitted, because it was saved before the student started the quiz. The solution is to tell students to clear their cached pages and restart their browser. There may be settings students can adjust to prevent cached pages in the future, and canvas recommends their mobile app for students using mobile devices (the most common source of this cached pages issue).
An alternate difference may be between students who finish quickly, and students for whom the timer runs out. If the student clicks submit, the submission is complete, and the assignment should accept comments. If the timer runs out, there may be more of a delay before the submission is recognized as complete. I have had some students whose quiz was still listed as "in progress" long after the until date, because they were stopped by that rather than the timer. It does not seem to interfere with grading, but I do not try to grade instantly after the submissions. It is possible that a quiz stuck in an "in progress" state might not allow comments because of the new student assignment view. The moderate tab has functions for you to manually conclude an "in progress" attempt, if that is the problem.
As an alternative, have you considered adding a "do not count towards grades" assignment after the quiz to accept the scratch paper photos?