Boolean Operation is not filling mesh I'm trying to make a cutout like the following (a hourglass shape) in an object.
But when I add the boolean it doesn't fill the mesh. I get a cut out like a cylinder instead.
You can see the inside of the object.

There is only a subdivision modifier on the object applied currently.
I've found the problem, it had to do with the Mirror modifier. When I created the object I deleted 1 face of the object that was on the inside. Which is why it was empty instead of filling.