I've successfully upgraded two machines from 16.04 to 18.04 without an incident. On a third machine the installation ran without reporting an error but did not demand a reboot - on rebooting the machine I received a 'reboot and select proper boot device' message and no longer have access to the installation.
I've tried using boot-repair from a live 18.04 install on a USB stick but the program did not give me a 'Recommended repair' option - it only gave me a 'Create a BootInfo summary' option, the output of which is here: https://paste.ubuntu.com/p/2rGh2drJQt/
Can anybody please help me gain access to my machine? Thank you.