Are you using a static IP? if not that would be the 1st thing to try.
what are the 3 LEDs doing when it disconnects?
many of the disconnects I have seen posted are actually just some services. with no response even to ping it make it difficult to diagnose
if it happens again try reseting the router to see if it helps
Rebooting the router is not the solution or even a way to determine the cause of the issue. THe fact that other devices on the router fuction without any problem and only the WD drives becomes unreachable says it all.
There is some ghostly stuff going on here with the drives.
the last time i encountered this poblem.
The leds in the back were normal, green and green blinking, no ping to drive IP (static from the router), no dashboard at all.