@Y-Phil what hair is that? Maybe I have it and can check. I'm still convinced that cast shadows is turned off. A lot of hair modelers make cast6 shadows off by default so their hair renders fast for the users. SAV did this regularly. It only takes a few seconds to check the actors (neck, head etc.) The second image you posted where you altered stuff inside the compound node still looks like it is not casting shadows. Look at the back of her neck under the hair. That should be dark but is just as bright as the front of her neck. The parts that people are seeing as "cast shadow" is diffuse and caustics bounce from the hair, not shadows.

W10, Ryzen 5 1600x, 16Gb,RTX2060Super+GTX980, PP11, 11.3.740