Shell stress results may be confusing since there are special rules regarding this element output. Most importantly, Abaqus projects and rotates the coordinate system (global or local) on the shell surface in such manner that Z axis is always coincident with shell’s normal vector. Stress in this direction is always zero.
There are also special purpose output variables for transverse shear stress components in shells called TSHR. You can request them before the analysis.
One more thing - you should be familiar with shell section points too. You may have to change the default top/bottom plotting if you want transverse shear stress values other than zero.