I had similar problem. After change disk on Aura Pro x2 not recognized by macbook. Till boot the machine using COMMAND+OPTION+R (helpdesk from OWC). Full instruction below: -Put the Aura Pro X2 into the machine. -Put the Apple drive into the enclosure (optional) -Boot the machine using COMMAND+OPTION+R (this is the specific key combo for High Sierra and above's Recovery mode) -From there you should see the Aura Pro X2 in Disk Utility.  -Erase/format the drive in APFS -Exit out to the main Recovery window -Then, you can install a fresh copy of the OS there in Recovery, and you can use Migration Assistant after it's done, to move your data, OR -Restore from Time Machine back up