If most of the students in your class are having an issue, check out this article.
On occasion, the AI may get stuck while one of your students is trying to submit a response to an assignment. If trying again isn't working, you can reset their submission to unstick them.
How to reset your student's submission
Resetting your student's submission will erase their responses so you may want to let them know to copy their answers first.
Go to your Submissions page for your class from the top nav links
Click the kebab menu (ellipsis) on the student's row in the table
Select Reset submission