Need to group 1 pivot table among 30

Hi all, I have a worksheet with over 30 pivot tables. My pivot tables represent pay bi weekly pay periods, but I need ONE of the pivot tables to group by month (for government remittances).

Problem is, when I group the WSIB pivot table by month, it then groups ALL the pivots.

I even tried to move the WSIB pivot table to a separate sheet within the same workbook and it still groups all of them.

Is grouping an All or nothing feature?

Thanks