Should have been du -xhd 1 /srv/dev-disk-by-uuid-F48E91208E90DD04/ without the space.
Code
root@NAS:~# du -xhd 1 /srv/dev-disk-by-uuid-F48E91208E90DD04/
2.4T /srv/dev-disk-by-uuid-F48E91208E90DD04/Anna
96M /srv/dev-disk-by-uuid-F48E91208E90DD04/Config
0 /srv/dev-disk-by-uuid-F48E91208E90DD04/Download
0 /srv/dev-disk-by-uuid-F48E91208E90DD04/Downloads
0 /srv/dev-disk-by-uuid-F48E91208E90DD04/lost+found
57M /srv/dev-disk-by-uuid-F48E91208E90DD04/Riccardo
2.4T /srv/dev-disk-by-uuid-F48E91208E90DD04/
root@NAS:~#
There should be more than 1 TiB of data in the 'Riccardo' folder!