Element.GetParts - some walls valid but not all

Hi there,

I am trying to separate a flattened list of walls into parts using the SteamNodes Element.GetParts node.

Some of the walls are separating just fine but others are returning Empty Lists. if I use the Parts.ElementsAreValidToCreateParts node it comes back with a corresponding result for the walls that are not valid for parts creation.

I am unable to diagnose what is causing the walls to be valid or invalid for parts?

Many thanks