Hi there!
I just tried to import your FBX file, and with some tweaks on the FBX import settings, I was able to import the whole mesh correctly:
- Uncheck Enable Nanite
- Check Tranform Vertex to absolute
I’m not really sure why it behaves that way with Nanite, but you can enable it back after it was correctly imported with the checked transform vertex to absolute. That’s probably the issue you had, although it has nothing to do with the fact that Unreal renamed some mesh parts.
Hope it helps 
