The report will work if the academic year is change to track attendance by Day Only (Configuration, Academic Years). The Day attendance was entered when the Academic Year was set to Day only. The Class attendance entries did not get created. At some point the Academic Year was changed to class or day. The report won't function the same if the Academic Year is set to Class or Day after the fact. It won't show the Day entries the same if they were entered when the Academic Year was set to day only.
To get this to work:
A. Change the Academic Year to Day only at least temporarily and rerun the report
B. Delete the attendance that was entered while the Academic Year was set to Day only and reenter now that the Academic Year is set to Class or Day
If the Academic Year is set to track attendance by class or day, classes will have to exist for the attendance to appear. Students will also have to be enrolled in those classes for the attendance to appear. The course records for those classes will also need to be marked to track attendance (Restrictions 2 tab of the course record, set by academic year and session).