There is probably a bug with the “As pin” option for node “Layered blend per bone” in persona.
When I use variables to control the blend weight between two blend pose, my filter bone is not consider.
This was fixed in 4.12. Also, you were close with where to ask on Answerhub. I converted your “Answer” to a comment. You can simply hit “Reply” or “Add New Comment” if what you’re posting is not an Answer to the original question.