Is there any blend mode beside Normal applied to layer? Can you post screenshot with Layers panel expanded and visible? It will be also useful to see WIndow > Brush Settings panel.
I can replicate. It seems like kind of a bug. If you create layer beneath and fill it with white, noise or anomalies (pixelation) will dissapear right? Like on your last screenshot, if you have layer beneath or layer is a background layer pixelation will not show up, if you have normal layer filled with black color painting with Eraser will display noisy or pixelated edges.