could you check the parameter promoting in Mat context.
I can extract any float value from a mat network, change this value in top level parameter window and see those parameter change live in the render window.
It doesn t work with a promoted node switcher. Parameter are working as expected but you need to reload the scene to see the result live of this node switch result.
If you try the same thing in a SHOP context : no problem working as expected everything is live any change in parameter are updated without a reload.
I'm still not familar with the not so new mat context, maybe something i don't understand on the Houdini side.