Hi, I've tried to inspect your 3D file, and it has several criticalities that put in difficulty many programs not only Moi3D, your curves are full of segments as if they were extracted from a polygon mesh, and this complicates the operation, you have to try to use simple curves and splines and possibly drawn with Moi3D.

In your file I have simplified the curves with the command "Rebuild" that you find at this link https://moi3d.com/2.0/docs/moi_command_reference10.htm#rebuild

I have not completely redone your model but I used your curves to generate new surfaces, but also the solid that you had created with the network of curves is technically incorrect.

For now I can do only this, since I do not have much time, but try to make simple curves and avoid building surfaces with too many curves as with the network, when you have to make complex parts you have to simplify the construction using many pieces to create a 'single solid.