it uploads backups to Onedrive. Your storage or settings may be preventing you from finishing them. go to https://onedrive.live.com/Options/DeviceBackups to check and see if you have too many or some you could delete to create a new complete one. I've found that when I did backups that didn't complete with an HTC One M8 it was only settings and app settings backups that didn't finish and minimally affected me.