Was playing around with the new plugin when I had the known transparency problem when two object are very close to each other. This can happen with hair, pockets on pants, shirts,jackets or when you want to hide some stuff. Normally you can change the Rayepsilon slider to fix this, but this can also create unwanted side effects like bad shadows from low geometry objects.
In this scene I have a shadow problem with the hair line. Many ways to go about that, but I use my favorite fix which is fast and that is to scale the scene. Under Setup I changed the scale from 2.6 to 10. This is just a quick fix I hope you can use if you run into this problem in the future.