I have connected the drive to another PC as the only drive other than a CD-ROM. Booted the 64 bit System Rescue CD, started the GUI then launched gparted.

Gparted saw just one drive of 3.64 TB, unallocated. I created a GPT partition table then an NTFS partition and shut down.

Now the drive is again connected to a Windows PC where it sees and has mounted the 3.64 TB NTFS partition.

That's good, one would think. Windows Disk Management and AOMEI both see a "phantom" 1.64 TB drive that doesn't exist. So there's still something screwed up with the drive. I'm going to fill the 4 TB partition and see what happens.

Finally got it sorted. Gparted on the Arch Linux System Rescue CD kept saying the backup GPT partition table was corrupted. Apparently clicking the option to fix it wasn't working.
So I thought, what if I change the partition map to something very unlike GPT? I chose Mac then created a new partition in the unallocated space. After applying that I changed it back to GPT and NTFS, then formatted it.

Finally! That has eliminated the 'ghost drive'. Could be that the live mode of that Ubuntu DVD doesn't properly support GPT NTFS over 2 TB and whatever it did to it while writing to it fouled up the partition table in some fashion to make Windows (and Debian Linux on Open Media Vault) see it as two separate drives.

So now I know, don't use a live Linux boot disk to write to an NTFS volume over 2 TB without first verifying that it can do it without screwing up the partition table of the destination drive.

I've named the drive Laz1 because it's been resurrected and it's Easter Sunday. I though about Hey-Soos but, nahhh. It's not that big of a deal.

Do you even know that your original drive was NTFS ? Since it supported both Windows and Mac it may have been exFAT which MacOS can easily read and write out of the box.

It was NTFS because I had formatted it and selected NTFS to delete what was on it rather than wait for deleting.

I wonder if your first post points to the real problem.
You said that the destination drive (after trying the copy) showed a 2 TB partition and 1.56 TB unallocated space.

IIRC the 2 TB limit was there with linux 32bit OSes and went away with the 64bit OSes.
I know Fedora was that way and I suspect Ubuntu is the same.

Is it possible that the Ubuntu version you were trying to use was 32bit ?
Ubuntu 18.04 LTS is available in both 32bit6 and 64bit versions.

I got the 64 bit ISO. Wouldn't have been able to read the source drive if there was a 2TB limit.

What may have caused the problem was the drive had a small 15 meg partition at the front of it. Could be that's something for Mac compatibility? It's not there now after fixing the problem. Something odd is that testing this drive and my other identical 4TB Seagate with ATTO shows differing performance. The other drive still has that 15 meg partition and it's slower.

I bought a new Seagate 6TB with a built in 2 port USB 3 hub. It has a 128 meg partition at the front. These little partitions show as being empty. Space for a Mac to install its disk driver? I'm going to copy everything off the other 4TB (not with this Ubuntu DVD) then nuke it so there will be just one NTFS partition and see if ATTO shows it matching the speed of the first one.