WD My Cloud urgent firmware issue

I have not experienced this issue in particular, but I have had problems where the connected drive would dissappear from the MyCloud.  I even tried turning on FTP and transferring that way.  I was able to transfer 3TB then after a while the MyCloud reported that the drive was removed.  For a test, would you mind turning on FTP and try copying that way.  The FTP credentials would be the same as your admin login.