ANSYS Workbench composite structure stress output

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So I have a composite laminate structure with wall thickness of 2 mm and maximum dimension around 600 mm. Material model is fully orthotropic with 9 elastic constants defined and fabric is assumed to be symmetric (E1=E2). Structure is modelled using shell elements and loaded with pressure and acceleration. I'm reading directional Y axis normal stress on a single ply (in ply coordinate system) and it turns out the minimum value is lower than the minimum principal stress. The difference is about 0.3%. These values are not on the same node but are on the nodes that are next to each other and both on the edge of the structure. How is this possible that directional stress has larger magnitude than the principal one?