Ohh, sorry, it's true it's late in Sydney 😄 , here in italy we
are still on the 21 🤣
Anyway, I erroneously thought that it would have been the same to use the original
model instead than the one with only the copy-pasted part.
You rightly showed me I was wrong.
Soo, uhm uhm, I'll try to work on a copy-paste part on another file and
reimport it on the original mode..
But that's a really crappy bug, since I am always careful to my geometry and
I clean and verify my model often.
Thank you Box!