HDX loosing all details of music on NAS share

I have a recurring problem with my HDX which loses the complete contents of music on my NAS.

This problem seems to have begun since the update to the latest HDX software which included the Internet radio facility.

My network consists of Draytek Vigor 2820n ADSL router which attaches to 8 port Netgear FS108 Gigabit switch which then talks via Powerline to another Netgear FS105 5 port Gigabit switch in my library where the HDX and HDX are. The FS105 attaches to HDX, NDX and a Wired for Sound ZP90.

The Draytek unit acts as the DHCP server and I use the BIND IP to MAC facility on the Draytek to ensure that IP assigments for HDX,NDX etc are always the same. The NDX and Wired for Sound ZP90 seem to have no issues.

The NAS is a QNAP TS419 Turbo and again always has the same ip. It is attached to the FS108 switch.

HDX does not loose physical connection in that it still recognises  the QNAP as a share that is active but says there is no music on it. A rescan fixes the issue and it finds the 9000+ music tracks on there and works ok for  a while. e.g. I rescanned yesterday and it was ok yesterday - check today and the HDX only knows about music on the internal drive.