There is potentially an SMB issue with Windows 10. I have found that changing the SMB setting either in the My Cloud or on my Windows 10 PC seems to fix the missing My Cloud in the File Explorer. Unknown how that change will affect file copying speeds though.
See the entry titled Method 6 in the following updated thread…
https://community.wd.com/t/compilation-of-windows-10-methods-steps-and-solutions/142576
