Same problem here, Sierra 10.12.6 on a brand new Macbook Pro with WD Elements.
Additionally, my WD Elements has started beeping every few seconds since I think the second attempt at reformatting I did. I didn’t drop/damage the disk in any way, it’s brand new.
The beeping occurs when the drive is attached to an external Mac keyboard (also new), which is attached to my MBP via an official thunderbolt-to-HDMI+USB adapter which is in turn connected the the MBP thunderbolt (because there’s no… USB drives). Nightmare.
The beeping stops when I attach the drive directly to an official thunderbolt-to-HDMI+USB adapter (so skipping out the keyboard extension). In either method of connection, backups fail as noted by the OP.
I’ve downloaded and installed latest drivers for “Mac OS 10.12” (WD v18.104.22.168), running the WD app does not recognise my WD drive.
At this point, I’m going to try BoilerJR’s suggestion and if that fails - never getting a WD drive again. I want safety in my backups, simple!