The drive passes the Apple Disk Utility First aid - says its ok. And I downloaded WD own utilities and it passes that.
So as I have repeated messages it can't back up to "Time Machine".....and also the thing has basically gone to sleep when the Mac goes to sleep and hasn't woken up. I truly think the discussion on the link above really is the answer as to why its not been behaving since I put it on the iMac Pro with Mojave.
My remedies would seem to be wipe this drive and make it a Carbon Copy Clone.... or (b) buy a different brand drive to set up as a TM - one that is compatible.
I am dealing with a WD support person who did answer my support request very quickly but it seemed obvious to me she knew little about Macs and Tm -- but I have sent all the snapshots she has asked for and I await her conclusions.
Jude
