I had try rebooting 3 or 4 time and wait 30 minutes between every reboot and of course, the usb key was correctly mounted by the nvidia shield.
From what I know, I think that when you had format your usb key to become a internal storage, you cannot change that with the shield, so it is why I reformat it with my pc.
In brief, now it work because now my usb stick is a removable storage. It work perfectly.
I think there is a problem when you want to move the server in a internal storage. It should be verify by Plex.
It is probaly why is was not working with this guy when he was trying with an internal storage, but it work with an removable storage.
Edit: Finally, it do not work ^^’
