When going to the Attendance by Photo page, students do not automatically load for a selected period chart that has an active class with students enrolled. 

Cause

An incorrect or old section is attached to the attendance by photo chart that was created.

Resolution

Correct the Default chart section association for the period. This can be done by going to Open Seating Charts.

For the period with the issue check what section is attached to the Default Type chart for the period. 

If the section is incorrect, delete the chart and recreate it and it will associate a new chart with the most current section for the period.