Why is my trimmed surface hollow?

[Kyuubimode]

hollow surface.3dm (738.7 KB)

What causes a trimmed surface to be hollow i.e. not generate a render mesh? How do I fix this?

[Piotr]

You’ve got self-intersection where the red dot is. Clean it.

I’d clean this as well, there are many proximities of this kind

[Kyuubimode]

Thanks, clearing the self-intersection fixed the issue!