Incorrect Von Mises stress

Hi all

I have a model which is a bracket made of 8mm-thick plates and isbolted to a fixed plate by four bolts and a 1KN load on the otherend .
I created four bolt connections and run the simulation. The maximumprincipal stresses are 96.2, 63.4 and 22.1 MPa, but the maximumresultant Von Mises stress calculated by the program is 290 MPa. Iassume this should be around 90MPa. I cannot justify the jump inmagnitude of stress based on Von Mises stress formula.
Could you please give me some advice in this regard?

Regards,

Reza KharraziSolidworksSimulation