This is what I found since owning this device. I no longer have it set up to automatically turn off (energy saving feature), because I was constantly getting device is offline from my WD Photos App. I would have to wake it up from my home network or reboot the device. Since I have done that, I have never received a Offline message.
My suggestion, reboot the device and change the setting for energy saving since it seems it was actually turning the drive off and making it OFF LINE to the WD Photos APP when launched and attempting to contact the NAS drive, it wouldnt wake up from the WD Photos or Mionet trying to access to it.
Once you reboot, sign out of WD PHOTOS and Sign back in after a few minutes and everything should be accessible.