Occasionally, Quizster will stop working as it should and you may not be able to submit assignments, grade, etc... This is often times the result of the browser (Safari/Chrome/Firefox) on an iPhone or iPad entering a crashed state. The best way to recover from this state is to force your browser (Safari/Chrome) to close using the directions at https://support.apple.com/en-us/HT201330. Alternatively, you can just restart your iPhone/iPad.
If you are encountering a frequent issue, please contact support at https://quizster.co