I’ve got the same issue… Really starting to annoy me immensely.
I have just had the unit replaced and have carried out all firmware updates. I have put 2 new WD Reds in for 6 TB and have started moving my data across from my portable drive back on to the unit. I have a drag and drop window showing the data moving across my own home network and it stopped at 70% and cannot access the WD EX2 drive anymore!!!
I cannot access the dashboard and I cannot access it from any other device (iPhone/iPad/external network). I have done a hard reset of the router to rectify, but nothing works. The only thing I can do and have done in the past to make it work is a 240 V reset on the device. This is not good for the drives, but without doing this it will stay offline.
There is no common action that seems to prompt the device to go ‘Offline’, sometimes it will work for a while before it does it and sometimes it’s pretty quickly offline. It’s a ridiculous situation!!!