It looks like Google has had a major update today (January 15th) and now the "Grade" (adding of the grades to create an overall course grade) is not working. Every student says "No Grade' despite evaluative numbers for each assessment being present.
Perhaps a function has changed names or the way a function works has changed.
I'm right in the middle of my exam block too :(
Sorry for the bad news. I hope you have time soon.
Thanks for a fantastic grade book. This has been a lifesaver!