Max. Von Mises stress Fringe vs. Measure

Hello!

I am calculating a truss simulation of a 3d Structure with L-Profiles.

I have set the idealizations for beams, constraint sets, loads, etc.

After the Statich analysis, I can review the Max VM Stress in Fringe model and it is 47 MPa

Then I have put some measures (Of Max VM Stress) in some critical points (or beams) and the Max Stress ist 54,1 Mpa

I have checked the Max VM Stress in the Study Status (where all the predefined Measures are shown) and the Max VM Stress is 52,9 MPa( I think it is near of my Measure, but I don't know really where)

Why is the Fringe model not showing the real Max VM Stress?

Thank you in advance