Most likely from your mesh being entirely too coarse. You probably have a situation where you aren't really representing a circle well because there aren't enough elements. Your stress results being blotchy indicate that as well. Put in a much finer mesh and rerun it and see what happens. If you choose a value that is the diameter/some integer for the mesh size, you are much more likely to get a mesh that is symmetrical. Also, use the curvature based mesher if you used the standard mesher.