On further review of your log;
You appear to be using a streaming service?
Most of the streaming services don't send fanart via Json to applications external to Kodi. The Kodi fanart that you see in Kodi is pulled straight from the service by the Kodi Addon (which obviously is service-service dependant)
(some do though Google Music addon for example)
Frontview does however check you music sources (already defined in Kodi) for extrafanart - and if present uses this on a cycle.
This provides a much better fanart experience. Although does need to be downloaded first.
For example for the song you were playing - it checks here for any extrafanart images
\WHS\Musik\Sunny Lax\extrafanart\
cdART Manager - automates these downloads for you.
http://forum.xbmc.org/showthread.php?tid=77031
It does create Artist directories in your music location however; for the extrafanart downloads.
I can look at checking for your particular service and pulling the fanart directly from it however - just need the details of the service/addon and a log with a few files being played to test/check.