The firmware update went fine. I tried to install 10.13.4 on and ssd connected via an Apricorn Velocity Duo. The install would get to the white screen with the Apple logo and at some point the screen would start flashing. I have a cloned drive, but when I try to boot from it the machine boot loops. This is pretty painful. I think I can roll back using recovery and time machine. If that doesn’t work I might be hosed. --- Post Merged, Apr 3, 2018 --- Also I can’t restore from time machine to the drive. I think I am screwed.