My external hard drive isn't working properly. It sometimes disconnects randomly, even while using a Y-cable (I tried the front and rear USB ports). I was able to copy all of my game data to it, but when I tried copying the game data from the hard drive back to my Wii U I received this message:
"An error occurred while moving the game data. Some content couldn't be transferred."
So now some of my game data is stuck on the hard drive.