USB drive is always properly mounted, but many times the Library is empty

Hi have Volumio on RPi 3 running on a Boss 1.2 player by Allo.com, and an external 2TB USB drive (M3 Portable by Maxtor) connected to it.
Everytime Volumio starts, the USB drive is always properly mounted on /media/Maxtor, and over SSH I can browse all the content of the USB, and I can see all the folders and FLAC and MP3 files. But many times the Library is empty, and if I go to Settings -> Sources, neither Update nor Rescan has effect, looks like Volumio doesn’t see the USB drive. The only way to make it work, is to restart the system, and sometimes it takes three or four tries, before the Library is populated, again.
Dmesg is the same everytime, I can’t find any error when I get the issue, here is the section related to the USB drive:
[ 5.172214] usb 1-1.1.2: new high-speed USB device number 5 using dwc_otg
[ 5.383179] usb 1-1.1.2: New USB device found, idVendor=0bc2, idProduct=61b5, bcdDevice= 7.10
[ 5.383192] usb 1-1.1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 5.383201] usb 1-1.1.2: Product: M3 Portable
[ 5.383210] usb 1-1.1.2: Manufacturer: Seagate
[ 5.383219] usb 1-1.1.2: SerialNumber: NM15L39N
[ 5.383881] usb 1-1.1.2: The driver for the USB controller dwc_otg_hcd does not support scatter-gather which is
[ 5.383891] usb 1-1.1.2: required by the UAS driver. Please try an other USB controller if you wish to use UAS.
[ 5.383902] usb-storage 1-1.1.2:1.0: USB Mass Storage device detected
[ 5.384820] scsi host0: usb-storage 1-1.1.2:1.0
[ 6.392854] scsi 0:0:0:0: Direct-Access Seagate M3 Portable 0710 PQ: 0 ANSI: 6
[ 7.744790] sd 0:0:0:0: [sda] 3907029167 512-byte logical blocks: (2.00 TB/1.82 TiB)
[ 7.745256] sd 0:0:0:0: [sda] Write Protect is off
[ 7.745268] sd 0:0:0:0: [sda] Mode Sense: 47 00 00 08
[ 7.745633] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn’t support DPO or FUA
[ 7.773532] sda: sda1
[ 7.775759] sd 0:0:0:0: [sda] Attached SCSI disk

this is exactly the same message in dmesg I get everytime, whether I get the issue or not.

Please note that I have a power supply for the Raspberry and another for the Allo DAC, while the USB drive only have the usb cable.
I just upgraded Volumio to the latest version, but the issue is still here.
Today I noticed that after manually restating the mpd service everything works fine, Volumio sees the USB drive and the library is populated.
How can I make it work definitively?
Thanks for your help!

Ping. I have this problem too. Would appreciate someone pick this up.