SM6 Error while Substrate Horizontal Blend 2 Metallic Materials

Today, i create a new Master Material, which should be able to Blend up to 3 different Materials together with Substrate Horizontal Blend - Node.

it works, but only for 2+ non-Metallic Materials. That means one metallic Material is fine but with more than one it prints the SM6 Error

i will show you now the Material Bluprint:

this section is the same for all three Materials:

for the Substrate Horizontal Blend-Nodes: