We were having a similar issue this was the response from Canvas Support and it did clear the issue up for us.

"You called Canvas Support today because you were working with an instructor who was grading New Quizzes short answer questions but the grade was not updating on the gradebook side. In the example that you were showing it looked like this was due to the course being concluded which would prevent the grades from being passed from New Quizzes. If you come across this issue again or have any additional questions, please don't hesitate to give us a call or email us at support@instructure.com."