Skeletal mesh precision issue

I have a super annoying problem when I’m converting static meshes to skeletal meshes.
Infact, there is a little (about ~1 milimiter but It is super visible in my macro plan) but noticeable gap between two forms supposed to be identical.

Before skeletal mesh conversion

After skeletal mesh conversion

There is even a worse issue with lightning for metalic part, when It is converted to skeletal mesh, it absorbs and reflect light in a completely inconsistent manner (darker rendering)

Before skeletal mesh conversion

After skeletal mesh conversion

Any ideas :bulb: ?