Student course grades are not included in the downloaded .csv file when using the Export Course Grades for Wolverine Access function. Using any of the other three download functions available on that page results in a file that does contain the course grades as expected.
The workaround is to download using the Export Course Grades as CSV button and adjust it to conform to the required Wolverine Access format by removing the header row and the column containing user names.
A concern with this issue is that this is a new feature that has received much positive feedback and this term is the first time instructors will be using it to move their grades to WA. So just when it is most needed the new feature is not working.
Create some GB items and assign grades to students on the site
Make sure "include in course grades" is selected for at least one GB item
In GB, click the Course Grades button
On the Course Grades page, click the Download button for the Export Course Grades for Wolverine Access option
The downloaded spreadsheet will contain student uniqnames but no course grade will show in the column next to the names