Can an instructor go back into canvas after a student has successfully submitted their work and adjust the exam settings, responses, and questions? What causes a student to resubmit their work after it was submitted successfully the first-time through canvas? Is it due to an instructor adjusting the format of the exam or question?
If an instructor makes a change to a quiz the submissions of prior students are not changed. The update occurs to a copy of the question. Successful submissions are not easily removed from canvas, and so that should be reported to support if it happened. The content can probably be recovered.