I also experienced the issue after upgrading from Kubuntu 19.04 to 19.10. I am also using LVM as other posters here. I solved the issue with the usual boot from live ISO + mount/chroot + grub-install.
I also experienced the issue after upgrading from Kubuntu 19.04 to 19.10. I am also using LVM as other posters here. I solved the issue with the usual boot from live ISO + mount/chroot + grub-install.