I have seen this problem before and was able to solve it under windows 7 but so far its solution eludes me under windows 10. It happens when you’ve two of the same model of western digital mybook drives plugged into the same pc. Both show up under device manager but only one can be seen in file explorer which formerly was windows explorer in earlier versions of windows and only one is seen under disc management in control panel.
It doesn’t happen if you’ve two drives of differing sizes from Western digital or two drives of differing brands.
If anyone’s encountered this and found a way to get that second drive to come online and become visible I’d love to hear about it.
thanks in advance.