Hi Tsee Lee,

Can you please submit a support ticket if you haven't done so already? This will allow our technical support team to take a closer look at the issue.

In the ticket details, please be sure to include the name of the class, the names of a few assignments that are showing this behavior, and the usernames of a few of the students that are affected.

Students may also need to clear their browser cookies and cache: https://support.khanacademy.org/hc/en-us/articles/115003233652-How-can-I-delete-cookies-and-cache-from-my-web-browser

Thanks!