Arnold doesnt render 2nd assigned Material
 

I made 2 Materials, assigned the first to the entire object, then selected some of the faces (the windowframes) and applied the second material to them (right mouse > assign existing material).
In the Arnold Render view, this material only shows up after hitting "Update full scene" several times.
When I render the current frame the material doesnt get rendered, instead arnold uses the first applied material.

In this Image: https://imgur.com/a/FI2f79G you can see the "Render Current Frame" Result. notice how in the viewport the 2nd material on the window frame is visible in a different color.

Hoping for any help, google didnt give any results. Thx in advance.