SYNOLOGY 213+ NAS - No Server message on nStream client

I have a SuperUniti physically wired to a Netgear 5 port switch which streams my music from my Synology 213+ NAS (2 x 2TB config) via a Virgin SuperHub2 (all hardwired Ethernet). Most of the time all is well using ipad 1 client or iPhone 5. However increasingly I am getting a NO SERVER message from all clients even the front panel on the SU but not always, and the only solution seems to either a reboot of the SuperUniti, Virgin Superhub2 or NAS (sometimes all is the only way to get everything working normally again). I have occasionally been able to just ping the NAS on its 192.168.0.9 assigned address from the Virgin Superhub2 web admin interface and this sometime fixes the issue and the NAS then re-appears on the network. Question is why does the NAS keep disappearing? The NAS gets its ip address via DHCP on the router and will work fine for days then suddenly disappears from sight. I have also noticed that the Virgin web admin tool accessed on 192.168.0.1 also often fails to display all the connected wired devices even when they are actually working normally, but on refresh then sometimes display normally for a while before failing again, all very odd behaviour, any ideas or is it just another rubbish router from Virgin?