Comment 24 for bug 1848797

I too had this issue today. My system is relatively simple:
1) I am using LVM
2) I was running 19.04
3) I was using an nvme drive (NOT /dev/sda as it likely expected)
4) To fix it I used the chroot method outlined on the Wiki, running both 'grub-install' and 'grub-update'

System is a brand new, never previously been upgraded 19.04 system with only this one drive and OS installed (no dual-boot). AMD Ryzen hardware 12-core, with a pcie nvme boot drive.

Think that's all I have for info to report... not the end of the world, but scary when you can no longer ssh into your server. :)