I believe the most recent update has bricked quite a few devices. After the latest update i could still access my shares but not log in via the web ui
I could see the ui log in page but my password was not accepted. It was the correct password as i did not get a password not recognized error. However when i tried a wrong password the UI responded with an error. So i assumed the device just needed a reset via the rear button.
Did that and not the device is completely bricked, im now copying the data from the drive via a usb enclosure to another NAS i have. Very disappointed.
I would recommend that no one else reset the device until WD release a fix or you could end up in the same situation.
My issue mimics yours. However, mine seem to start right after a hard shut down - pre firmware update.
We had a power outage and the drive went down hard as I do not have it powering off a UPS - just a surge protector. When the drive rebooted my Mac could no longer mount it. The two WIN 7 machines on the network mounted the drive no problem. I contacted WD Support (WDS) and got a silly response.
Right after this I noticed the firmware update and installed it through the Dashboard. Then my Mac seemed to be able to mount the drive however my file access was read only. WDS then suggested a quick Factory Restore. I resisted this as I had around 600 GB of unbacked up data on the drive. WDS indicated that this was the only fix. So, I backed up the info which took a few days and then the UI broke just like you describe. As a side note between me seeing the mount and finishing off the backup it seems the mount is now full access again.
Also my WD 2go access broke somewhere along the line.
I am kicking myself now for not switching on the ssh permissions as I have done a bit of hunting and it looks like there are a few options through ssh that may result in a fix.