I’ve had this happen a few times and it’s seriously annoying.

Basically, I decide to go back to my Debian testing install, realize it’s been a while, so I should run update, and that somehow borks my Grub stuff.

I don’t know exactly what’s going on, but this worked:

Boot up, but select to boot to Ubuntu instead of Debian.

That should show all of the Linux installs. Log into the correct Debian.

In there, I did the following:

sudo grub-mkconfig -o /boot/grub/grub.cfg

Then:

sudo grub-install

That seemed to fix it. I don’t know why it’s doing what it’s doing, but it’s annoying. I suspect that Debian testing is overwriting the above location,