The same thing happened to us. A teacher called us, indicating that the scores on the right were not updating even though they were clicking the "Update Score" button. I’m sharing what the situation was and the solution in case it helps others.
At our institution, we use the Term option to "conclude" courses. Initially, the term was set to end on December 17, and students would have access until that date. But when that day came, I received calls from teachers saying their courses were no longer visible and they were still grading final assignments. So, I corrected the Term end date, extending it to December 20, but I left the student access date as December 17 because I didn’t want students to continue having access (you can set different dates).
After that, the teachers could see their courses again, so I thought everything was resolved. However, on December 18, I received a call from a teacher experiencing this error and who was also unable to edit assignment groups.
In the exam, I could update the points for the students' responses, but the score on the right didn’t change.
So, I went to check the Term dates within the course itself and noticed that the end date was still set to December 17, the student access date. I went to the Term section and changed the student date to December 20, which updated the course's end date.
This change allowed me to update the scores in the exams since the course was no longer “concluded.”
Please note that you need to be an admin to access the Term area; teachers don’t have access to this section.
You can find more information about Terms on this page: How do term dates, course dates, and section dates work in Canvas?
Hope this help!