Hey there
This problem was reported by many users and WD never did anything. The firmware upgrade usually breaks it.
I never heard of anybody who brought it back online and the WD people won‘t help.
I can only link you to this thread: Solution for WD My Cloud Offline
The Video I linked there helped me to recover all the data. It‘s a lot of manual work, but it works. Note that the Python script is meant to be used on a drive with only one user. If you have multiple, it‘ll still work, but you‘ll need to run it once per user with updates parameters. Since you seem to be a techy you‘ll figure it out as I did 
After that: Throw the garbage away and buy a good (and real) NAS as I did (Synology for example)
