Excel: how can fix strange error in sum function?

Question

I have the following problem in Excel: I want to create a sum from positions. This happens dynamically by always finding the sum of all positions belonging to the order at the first position of the order and adding them up.

This actually works with the formula, but I have a very strange error with the following formula:

=IF(D4<>""; SUM(M4:INDEX(M:M; IFERROR(MIN(IF(G5:G$1048576<>""; ROW(G5:G$1048576))); ROW(G$1048576))) - 1); "")

In the first order, when I sum up 11.62, I suddenly have 11.41. In the second order, the sum only differs by one cent. Can someone explain to me how this can happen? I don't see any logic here.

You can see the Problem here:

Thank you for all ideas. :)