NAS mounted but suddenly no files

Dear fellow Volumionatos,

I’m encountering the strangest thing. I’m streaming with a RPI 3 + digione with a mounted NAS now for almost a year but sometimes suddenly the music files are vanished in the GUI, I can’t play any music and then… a couple of days later suddenly they appear again. But now… for a week… as you can see at the screenshot… no music, no albums. Update files will not bring them back and I really dont want to do a fresh scan from scrap as it will take days.

when by ssh volumio@ipadres cd /mnt/NAS/Muziek en then ls I do see all the album directories.

Can someone please tell me what’s going on?

Best regards from the Netherlands,