I had this problem and tried multiple re-boots and system resets but had no success. I finally solved the capacity issue in the dashboard by turning off the DNLA and itunes media servers and then rebuilding the content database. I’m not 100% sure if this was the solution. Perhaps it was coincidence. Nevertheless it is worth a try.
See under: General - Cloud Access - Configure - Content Database - Rebuild
As I said before you may need to leave the device for a day or so to stabilise.
If this doesn’t work you could disable the media scanning service if you are confident to SSH into your MyCloud. You should do this anyway after you manage to downgrade the firmware.
See this post:
http://community.wd.com/t5/WD-My-Cloud/Hidden-wdmc-directories-created-by-mcserver-and-photodbmerger/td-p/682091
