I recently bought a 6TB My Book. It was missing the USB cable so I used the cable from an older 3 TB drive. I started to have intermittant issues - the macbook pro would not recognize the drive. I used the disk utilities and they indicated a problem. Then the drive would come back OK. I got a replacement USB cable and connected the new cable and as well as the AC power that came with the new drive.
It seems to work OK now. I’m curious whether the USB cable for the 3 TB was different, causing some issues. Or will I expect issues down the road.