Top Layer/Solid Infill Bulge
I'm not sure about other slicers, but Cura has an option called Skin Overlap that defaults to 5% and causes excess material to be extruded beyond what actually fits in the skin (top/bottom &quot;solid infill&quot; surface) area. If you only have a few top layers it probably won't push the outer walls out and will just build up a rough top surface, but with more than a couple it's likely to start making the walls bulge out because there's nowhere else for the excess material to go. I've gotten dramatically better print quality since turning this setting off (0) and doing the same for Infill Overlap.