Glad that you complete the upgrade well. Best way is still CLEAN the HDD with diskpart and create a copy of backup data from SSD.  The boot manager doesn't like two identical bootable drive regardless of drive letter.  Why creating problem for yourself. 
I am trying to upgrade my four year old XPS 8930 from a 1TB HDD to a Samsung 980 Pro PCIe NMVe of 1 TB. I am comfortable doing basic things like upgrading ram but I am just a step or so above novice level when doing this level of upgrade. I have already made a full backup of my HDD disk with Macrium and have also created a rescue USB disk with Macrium and also a  Windows recovery disk on a USB.  I read the  posts on this forum and they are very helpful, but I noted a difference of opinion on when to install the SSD. The written posts appear to indicate that it is installed right after changing the BIOS from RAID to AHCI, because the Samsung SSD needs to run under AHCI for the computer to recognize it.  However, in a Youtube video from George Sops he installs the SSD before switching to AHCI and uses diskmgmt.msc  to initialize the SSD as GTP partition . After he changes from RAID to AHCI he then uses Macrium to clone the HDD to the SSD, which is the same as the information here.  What is the correct process and when to install the SSD? 
XPS 8930, from HDD to SSD NVMe, what step to install SSD?