With one student, one teacher, and performing the export as Admin that is also enrolled into the course as teacher. If you go into Grades, you see all grades and course total calculated correctly. Click Export table, unchecked include feedback in export, preview rows = 10, grade = real, grade export decimal = 2, and select all grade times. In this case there is only one Offline activity and Course Total is selected. Click submit..

Preview shows a "-" for course total and export reveals the same thing in the course total field.

PS> Theme alignment issues with sub tabs