I used to have continuous problems with the Safepoint procedure failing. The procedure would come to a stop for no apparent reason. Eventually I realised that this was when there was not enough space left on the back-up medium to continue. The MyCloud error message does not indicated that I had run out of space and the system does not check the available space before starting the Safepoint run - come on WD wake-up and smell the roses.
To solve this issue I now always format the backup medium before I start. This deletes all the old data and now the Safepoint runs cleanly every time. Just to be safe I keep two back-up devices and rotate these.