I suspect the mismatch between days in the year and the timetable is causing the problem.
For reference, if you set a homeroom, (when it is (re-)implemented), the attendance for the homeroom period is used to determine if the student was in attendance for the *day*, as opposed to just that period. This isn't relevant in post-secondary or lots of other cases, but in US schools, at least, it is an important legal requirement.
I suspect the mismatch between days in the year and the timetable is causing the problem.
For reference, if you set a homeroom, (when it is (re-)implemented), the attendance for the homeroom period is used to determine if the student was in attendance for the *day*, as opposed to just that period. This isn't relevant in post-secondary or lots of other cases, but in US schools, at least, it is an important legal requirement.