Library loading fails

[Nutul]

Looks good to a layman like me:

file "/mnt/NAS/Music/Jazz/Bill Evans/Everybody Digs Bill Evans [1958]/10. Bill Evans - Some Other Time.flac"
/mnt/NAS/Music/Jazz/Bill Evans/Everybody Digs Bill Evans [1958]/10. Bill Evans - Some Other Time.flac: Audio file with ID3 vers
ion 2.3.0, contains:FLAC audio bitstream data, 16 bit, stereo, 44.1 kHz, 16334052 samples

The problem is that it has id3v2 metadata tag; probably your tagging software has made a mess (let me guess... iTunes?)
The files do play, of course, but the engine responsible for the cover-art extraction cannot find it, as it expects a Vorbis Comment in a flac file, and not the id3v2.x, which is more typically found in MP3s.