Hello @EllenB
Are you using an internet browser or the teacher app to grade these quizzes? It is likely your internet browser and we recommend clearing the cache and cookies or trying another browser.
In Chrome
On your computer, open Chrome.
At the top right, click the three dots
Click settings
On the left, choose Privacy and Security
Then, clear browsing data
At the top, choose a time range. To delete everything, select All time. I suggest at least 4 weeks
Next to "Cookies and other site data" and "Cached images and files," check the boxes.
Click Clear data.
If you are using the Canvas app currently we also recommend doing the same thing:
What Student app options can I manage from my iOS ... - Instructure Community
If that still doesn't fix it, you'd want to speak with Canvas Support directly as that is abnormal behavior.
Because of the complexity of the issue, and the concerns for privacy, it would be best if you contacted Canvas Support directly to pinpoint the source of the issue and provide a resolution:
How do I contact Canvas Support? - Instructure Community