I encountered similar issues with an Aura 2TB SSD in my Mid-2014 MacBook Pro Retina. Many painful steps later I 1. upgraded to Mojave on the old SSD; 2. Created a bootable USB with Mojave; 3. Moved the Aura 2TB to the Mac and the old Apple SSD to the Envoy enclosure; 4. booted (using Cmd-R) and then installed Mojave on the 2TB from the USB key; 5. replaced USB key with Envoy external drive, rebooted, and used Mac Migration to copy files from the Envoy (the old 500GB SSD).
Before this I had tried (after step 4) to recover from a Time Machine backup I made but after 24 hours of TM in “Preparing Backup”, I cancelled this and went to the step 5 above.
So far (fingers crossed!) I’ve been running 2 days on the Aura 2TB SSD with no problems.