Look at the film as it washes. You will see tiny bubbles on the film caused from air entrained in the wash water. This can cause uneven washing with resulting dots of brown from retained hypo. We called it "measles". So, some sort of agitation should be used even in the wash. I just remove the reel from the tank and tap it a few times, then return it to the wash tank. I do this every time I see the bubbles accumulate.
This is not well known.