This can occur when a block is scheduled more than once in a given day. To verify:
  1. Go to onRecord > Procedures > Schedule.
  2. Select Master Schedule.
  3. View the date(s) where the duplicate attendance appears, and look to see if a block appears more than once.
Duplicate blocks in Schedule

Because the classes tied to the block (Homeroom in this example) occurred more than once on this day, attendance would be recorded once for each section. If the Attendance Record Method is set to be recorded Daily from a class that would meet in this block, the student would have multiple Attendance of Record entries for that date. If this is set to a specific Meeting Time, then only one Attendance of Record would be listed, with the second displaying as standard period attendance.