Your polygons are not planar - Shell modifier converts the model to editable mesh instead of editable poly, which shows faceting on non-planar polygons. You can hit "make planar" in editable poly or assign smoothing groups to the polygons to avoid this happening.
hello, can anyone help me figure out why I am seeing creases in my polygons after using the shell modifier or what I can do to avoid this? I need those polygons to look flat after I apply the shell modifier. Thanks in advance!