From the full solid model I made a symmetry constraint, so that I ended up with half of the solid model. The results is the same for these two (same meshsize). But when I simplify the model further with a part of the model made with shell elements, I end up with results that dont match anymore (VM, P1, P3). This new model with shell elements (2 mm thickness - midsurface) has a symmetry constraint and shows no sign of rotation over the plane of symmetry.  

There is a pressure load on the inside of the cylinder and the whole model is influenced by gravity. Foundation bolts are used as fixation.