It seems like there is a bug when you try to paint with Automask tool to existing Automask mask. After you finish the “first paint” of mask, then if you paint more, the mask looks fine, however adjustments are performed only to the “original first mask area”. Eraser is probably ok, but when I tried to repaint erased mask again, it doesn’t work (blue mask is okay, but adjustments are restricted to the first mask painting only).