I can't get difference Boolean to stop being hollow. Intersect boolean is solid but diference bool is hollow on both fast and exact solvers.

Here's the problem:

Here's the geometry:

Here's the bool object:

I can't get difference Boolean to stop being hollow. Intersect boolean is solid but diference bool is hollow on both fast and exact solvers.

Here's the problem:

Here's the geometry:

Here's the bool object:

Project file: