I had this issue and it was because I told grub to support dual booting from two different disk drives (one of them USB) and then I removed the USB drive. Linux-boi still tried to enforce booting from the now not-connected drive.

I can’t remember exactly what I did, but there may be something about a systemd unit which can be removed/disabled - or maybe I did some fishing around in fstab to remove the drive it thought should exist but wouldn’t always (and then probably did an update-initramfs -u or similar.