COUNT formula selectively working?

I made an attendance schedule for a nursery, it's supposed to allow me to check who is in what class depending on the month selected in the dropdown menus in A1/B1.
Zoomed in table.png


Then at the bottom is another table that counts how many kids are in each class, each day.

For some reason whenever i select a date in the past, the COUNT formula in the bottom table stops returning values... except for Thursday and Friday - despite them having an identical formula to the other days.
Zoomed in for August.png

The formula is as follows
=COUNT(FILTER(Attendance[Thursday], (Attendance[Thursday]=1) * SUBTOTAL(103, OFFSET(Attendance[Thursday], ROW(Attendance[Thursday])-MIN(ROW(Attendance[Thursday])),,1))))

Can anyone see where i've gone wrong here?

Attendance for Excel.xlsm

(Also, if anyone has any ideas/templates on how i could streamline any of this process please share! I've worked so long on this sheet that i can't see anything anymore)