This issue has been resolved and only impacted instructor users from 4:35pm until 5:47pm ET on September 9, 2019. Thank you for your patience while Canvas engineers worked to resolve this issue. For more information and the detailed resolution timeline, please see the Canvas System Status page.
Some users may have experienced "500 errors" within Canvas beginning at 4:25pm ET this afternoon, September 9, 2019. This service degradation currently affects only the quiz preview option in Canvas courses, so it is only impacting instructor users. Quiz submissions for students are unaffected, so students should not encounter trouble submitting quizzes.
Canvas engineers are aware of the issue and working towards a resolution. Thank you for your patience. For more information and updates on the situation, please see the Canvas System Status page.