Hi,This seems to have happened to me too. But I just upgraded my Debian unstable around the 5th of May and got a grub update. After the upgrade I could not boot into Debian again. When I tried it just failed into memory check and reboot.
I have an Dell XPS 15 9560.Setting GRUB_TERMINAL=console and running grub-install and update-grub got the system up and running again.
Jens