iPod Classic 80Gb appearing in OS X and Windows but no more on iTunes 12.0.1.26.

Since a few days, my iPod Classic is not appearing in iTunes Sources anymore, but appears in OS X and Windows.

I just tried all the troubleshooting steps from Apple Product support, including uninstall and re-install of the full iTunes and related software.

My other devices (ipod Touch, iPod Nano, iPhone) all work well and sync on the same computer.

I tried reseting the iPod, connecting on disc only mode, different cables, a lot of computer reset....

The iPod is working well as HDD (copy and delete of files al OK). It is also working well to listen to all the music already on it (from last sync).

I am not sure but I think the last time the sync worked I did a restore.

Anything else I could try? Any post or not well known procedure ?

Thanks.