Volumio 3 NAS source empty despite mount works and files visible in shell

I’ve just installed Volumio 3.173 on an RPi 3B+. I’ve added a NAS CIFS source named “media”. It’s visible on the source list, but it’s completely empty. Tried rescanning, it doesn’t do anything. I enabled SSH, logged in and I can see my files in “/mnt/NAS/media”, so the mount itself works. The files are in a directory hierarchy, not directly under the mount point, but I assume that shouldn’t be a problem.

Any hints are greatly appreciated.