One day, we will get there…
I found a somewhat vague post, it said ‘it’s in the build options on the asset’.
What I glean from this ( I’m not at a machine and can’t check ) is that you should be able to double click your mesh ( the one that doesn’t like the material ), which opens the mesh editor. In the mesh editor, I think there should be ‘build options’ and there will be something about ‘Build Adjacency Buffer’.
Fingers crossed…