We had someone report that after migrating to an external drives, it would not boot. He resolved it by doing this:
I got the info from here:
I simply deleted the entire in MountedDevices and then the MountedDevices itself and all was good. Without this last step the system would hang.
So before cloning simply set the BootDriverFlags(as in the video) and delete MountedDevices.
We haven’t been able to test since we don’t have a system in that state, but if it works for you, let me know and I’ll add it to the setup doc.