we all seem to have similar problems, see my post about remounting shares.
I figured out that volumio has problems if during it’s awake the NAS with the music goes to deep sleep/turns off. If you take a look at the network traffic at the point after the NAS went to sleep, you will see that volumio sends out ARP packages. He tries to figure out, what happened to the share. After some time it gives up and dismounts the share.
If you then start the NAS, I do this by sending a WOL from volumio to my NAS, the playback can not start until you remount your shares. In my case I remount the shares over the same script that woke up the NAS.
I would be great to have an option inside volumio to send a WOL and then remount, it would be cleaner. But my hack works as well and plays a nice starting sound to let you know that the NAS was off, until you wait for playback !