Wrong Subtotal in Pivot Table Distinct Count

Hi there,

I am encountering a problem with Pivot Table in Excel. I am trying to get Subtotal of Distinct Counts, but the manual total of the Distinct Count is different from the Subtotal done automatically by pivot table. In the attached picture of the pivot table, you can see that "Blue" is showing a subtotal of 15, while if I do it manually, it adds up to 16. Similarly, "Red" has a subtotal of 15 while if I do it manually, it adds up to 20.

I am unsure why this discrepancy exists and how to solve this problem. Has anyone else experienced this issue and found a solution? Any help would be greatly appreciated.

Thank you!