What does "Shows nothing" mean? Was the device not visible at any level in DU at all, but was not only visible but formatted in the enclosure? If so, that result seems to target the cable in the MBP. But then you said you booted from the external drive and, "Opened DU and the new SSD mounted internally is there." That result says the cable was good, at least at the point. But then you said. "Put the OEM back inside." I thought it WAS inside, or are you talking about some other "new SSD mounted internally?" Then you said, "Went back to the new internally and OEM in the encosure and target booted up fine. Went back to DU and tried to image the OEM from the external enclosure onto the new internal SSD and it keeps failing." Sorry, but at this time, I'm totally lost. Did you put both the original and new SSDs in the same enclosure? Maybe if you list out what you did, in detail, in order, so that we can see what worked and what didn't, we can suggest what to try.
Oh, and why, if you could see the new SSD when booted from the original in the external enclosure, didn't you go ahead and install the OS and migrate back to the new drive then? Was there something that triggered you to put the original back in?
At this time, the most likely issue is an intermittent cable to the drive in the MBP. It's worked with both drives and failed with both drives, which makes it very suspect.