I updated my MacBook to OSX 10.11.5 yesterday and not the My Cloud drive is basically unusable in Finder.
It is so slow and some folders never even show any contents.
I have rebooted the Mac, the router and the My Cloud drive and it’s the same. In the iOS app and on my Windows machine everything works fine.
I have the My Cloud pulling a static IP address and the way I connect on my Mac is to go to “Connect to a server” and use that address.