I have a Octominer B8Plus motherboard and it works fine with the mSATA SSD, but I really need to boot off a USB thumb drive with Ubuntu on it. I can't get this to work.
It just says "Reboot and Select proper Boot device or Insert Boot Media in selected Boot device and press a key".
Screenshot:
https://imgur.com/BMef7iLThe odds are you dont have it formatted correctly. I have a bunch of this case and with a proper boot usb it works 100% of the time. Just for grins use etcher and format a usb with smos on it and see if it boots.