There are many factors that affect the copying speed to and from the My Cloud. See the following link for a brief discussion on the various issues.
Did your Mac update to El Capitan recently? If so there is some sort of bug in that Apple update that is causing problems with My Cloud access and file copying. Use the search feature of this subforum (magnifying glass in upper right) and you’ll see the Mac/El Capitan issue discussed in numerous threads.
