I see this behavior with this kind of round pieces...bottom and top layers are missing some material (one "round). Extremely annoying. I can't find any way to fix this. Different layer thicknesses aren't helping. Any ideas?
Are you using concentric for the external fill pattern? If so, then you can make the edges meet up perfectly by making a slight adjustment to your extrusion width. Go to the Extruders tab, set the width to manual, and slightly adjust the value until the perimeters meet up perfectly in the middle. Usually you only need to make a tiny change such as changing the width from 0.4mm to 0.42mm or something similar.
Well, that was easy I tried shortly to adjust the width, but it has to be made for every piece (dimensions vary), so I just use rectilinear and avoid the whole problem...THANKS!