I have a teacher getting this error on one of their courses when trying to sync grades. The error only references the course name, no specific assignments. I can see there are 2 students in the course that do not have any sort of final grades, I am not sure if that is relevant. I will attach a screenshot of the error. I have not been able to find any answers here or elsewhere online so any help is appreciated, thanks.
The most common cause of this in my experience is a student being enrolled in the course after the due date of the assignment that is trying to sync. If you download the error log it should give you some more information as the to specific user. I'd be happy to assist if you can share a link to the course.
If you are able to locate that information, you can resolve the error by moving the due date of the assignment to being later than the date that the student was enrolled if those circumstances apply.