[jmbach]

Did you run a complete erase (write zeroes) followed by a complete read with WD Diagnostic? Even though the drive might be new, there may be flaky areas that get remapped after first write. This may cause your issue. There is always a hiccup that could have occurred during the copy process.

I had an issue where I copied my 3 TB Roamio drive to a 4 TB and got the Red Screen of Death. Repeated the copy several times using different combination of docks/connections with same result. If I did a KS 57 I got the green screen boot loop. In this case a KS 58 fixed the problem. Then when I analysed my 3 TB drive, there were a couple of sectors that were going bad. After running WD diagnostic full read and write about 3 times before I got zero errors and forced remap of the flaky sectors, I repurposed the drive in another unit and has been running fine without incident. (Although I admit I still periodically check it for errors with a full diagnostic read)

 

[jmbach]

For a normal Roamio drive the 'i' is not needed as it only purpose is to copy the alternate partition contents. Since in a Roamio these do not contain any relevant data (they are usually all zeroes and if not zeroes, it is just random bytes), using it is not necessary. That being said, not sure why it did not work for you using -ai as it should produce the same output as -a in a Roamio.
Using WD Diagnostic to do a complete erase of the drive would have been a whole lot fast as in several hours than using dd.