Second 6TB Thunderbolt is ejecting while copying files

I’ve been using a 6TB Thunderbolt for 3 months without any problem. Got a second one and daisy chained to make a backup of the first one but I can not copy files to it. Macbook Pro ejects it after 10-15 minutes copying starts.

Called Apple, and WD and no solution. It does not eject while NOT beeing written on and it is NOT a defective unit because I replaced it twice. This is the third drive doing it.

What happens when you try to connect it directly to the Mac?

I’m having a similar, possibly related issue:

I have a Western Digital USB3 external hard drive (attached to new MBP Retina) that seems to randomly “eject” itself when I’m trying to back it up via time machine. When this happens, I can’t even shut my machine down properly.

The backup process will run for sometimes 30 minutes or more. But, it’s as if, at some point, the drive just can’t be found. I get the message “this drive was ejected improperly”. When this happens: my machine won’t shut down, disk utility won’t run. I have to press and hold the power button to force a shut down. Any ideas what’s going on here? A MBP Retina issue? A USB3 issue? A western digital issue (although this drive has been functioning fine on old MBP)?