I've got a few STLs generated with OpenSCAD with a font, and I noticed the letters that have curves don't render correctly (O and B) and also the inside of A. I don't know enough about STL files to see what's not working correctly.

I had to zip the STL to upload it.
windmill-VIOLET.stl.zip
I've got a few STLs generated with OpenSCAD with a font, and I noticed the letters that have curves don't render correctly (O and B) and also the inside of A. I don't know enough about STL files to see what's not working correctly.
I had to zip the STL to upload it.
windmill-VIOLET.stl.zip