How to fix an issue with a report filter

Hello,

I am unable to add a filter to my report block. Please see details below:

The variable to be filtered is GRIR_Email, formula is

GRIR_Email = =If([PO_Line_Age])>=(([Pay_Terms_Days])+15) Then"Yes" Else "No" ForEach([Material - Vendor (Key)];[Purchasing document].[Purchasing document - Key])

This variable has only 2 values viz. "Yes" and "No". With No filter on the report, it displays 38 pages of data, however, whenever I filter on "Yes" it only shows 1 when it should show 20 pages atleast.

Would anyone be able to help me with this issue?