help on thickness

 From:  monica (MFRONTINI)
6523.6 In reply to 6523.5 
Ho cantato vittoria troppo presto....I sang victory too soon.
I had to reduce the size to reduce the price to have it 3D printed in ceramics. I needed to keep the thickness at 0.6cm.
I went thru the exact same process with the newly sized profies but I didn't get the same result.
The space between the inner part and the outer part is empty.

Can you please explain why and how it can be addressed?
Thank you
Monica