We know that for post-tensioned members, before tendon grouting, the net section is used; while after grouting, the transformed section is used.
So the section properties before and after grouting are different, therefore the stresses are different too.

But in CSM manual $2.4,

All construction stages that cause changes of stresses have to be considered. Therefore
construction stage grouting / extrusion (CS: x2) is not necessarily to be computed, due to the
fact that the grouting mortar causes no changes in stresses.

I guess it is noticed there that grouting itself does not case any loads, so if cs:x2 stage is not calulcated it is no problem, but after cs:x2 stage brutto section properties are used.

This is the official Sofistik Verification Example:
DCE-EN17: Stress Calculation at a Rectangular Pre-stressed Concrete CS
verification.dat\dcbenchmarks.dat\dce-en17\stress_prestress.dat
I add “CSM” in it.

At mid-span of the beam:

Hand calculation & AQB:
dead load moment = 1250 kNm
prestressing moment on net section (before grouting)= -1435.91 kNm
prestressing moment on transformed section (after grouting) = -1406.11 kNm
on net section, moment = 1250-1435.91 = -185.88 kNm, the bottom stress = -4.82 MPa

replied to my self
The stress in transformed section in CSM is correct, because the stress before grouting is “locked in” the structure, it won’t change after grouting.