Problem with the new experimental material layering system

Hey Guys,

I tried to get into the new material layering system which ist still in experimental phase in 4.20
My problem is that when I add a third material into my layer stack the whole material goes to default.
I thought maybe it has to compile first but that’s not the case.
As you can see in the pictures turning of the third material “solves” the problem.
So why is the third material messing up the whole thing?

Unreal often crashes when changing to many parameters in a short amount of time but I think this ist just because the feature is still experimental.
So no real problem here.