I have My Book Duo WDBFBE0160JBK-NESN and had this issue on High Siera on MacBook Pro and now I see the same issue on iMac on Mac OS Mojave.
After computer wakes up I see multiple, two or three “My Book” drives in finder, if I click on a right one I able to navigate in drive and open files. But If I click on a wrong one finder hangs and not responding.
When finder freezes even Disc Utility become disable It can’t find any drive at all.
I noticed that in Energy Saver settings I had selected “Put hard disk to sleep when possible” will try to disable it and see will it fix a problem.
But it would be very inefficient to keep drives work when they are not in use. I guess it will decreese their life time.