Discrepancy between Plate Stress Result and Cut Along Line Result in STAAD.Pro

Hi,

I am currently modelling a one way slab with fixed support in STAAD.Pro CONNECT Edition V22 Update 2. I want to check whether the bending moment (local MY) obtained using plate stress contour and cut along line agree. I cut the slab using line in global Z-axis, and then selecting Stress Type: Mt-Line  to obtain the MY.

However I found different values between both methods (see picture below)

Can anybody explain?

Thank you. 

File attachment:

Result Along Line Verification Model v1.STD