Correct, at 100% infill all layers should be solid. Then maybe you still have a slight underextrusion. Did those signs of overextrusion happen in the 1st or 2nd layer? Then ignore them, or increase your head about 0.05mm maybe. What's your nozzle size? If 0.4mm or 0.5mm try layer heights of 0.25mm or 0.3mm.