The process was :
- rip vinyls to computer
- export file (cut/paste) to storage
- copy from storage to external drive (or the other way, drive 1st then storage).
The file/folders structure was ok, the folder/tree size too. But when trying to play file, it open and then nothing happened.
0 size files...

So now even for important copy, I use something like Robocopy or a RELIABLE tools for cloning data (no super/ultra/uber/copier), no more OS finder/explorer copy of files that are precious. Never !