Difference in values between relative periods and fixed periods

Hello all,

I have an indicator in DHIS2 which when I display it from two different period types I get different values.

The top table is made from the relative periods (Month of this year and current year), and the bottom table is made with the fixed periods (All months from January to December 2020 + the year 2020). When we observe the two tables, we immediately notice the differences in values ​​(Example in September 2020). What is the cause?

Here is the composition of the indicator in question: