Not a single entry for crypttab, and you read it with root privleges?
Does this file exist on your system:
ls -lh /crypto_keyfile.bin
Grub always prompted for a passphrase? Even before you destroyed LUKS key slot 1?
I thought you switched to systemd-boot, because of how slow Grub is at decrypting the key? What happens if you try with systemd-boot now, after having destroyed the extra key slot?
Systemd-boot was retrieving the key file from somewhere if you could decrypt without your passphrase.
Last place I would look is under /etc/mkinitcpio.conf
Look for a line that reads
If such a line exists, comment it out or remove it.
What this does is load the key file into the initramfs (like a “mini” filesystem that lives and runs in RAM), and so the boot-loader has a filesystem it can work with and retrieve files, if needed, before you get access to the real root filesystem.
Commenting out the above line and removing the file /crypto_keyfile.bin should remove any traces of this behavior.
Don’t forget to rebuild and update.
sudo mkinitcpio -P
Also check out systemd-boot config:
sudo bootctl list
Alternatively, check the config file(s) under the folder “[esp]/loader/entries/” in your EFI system partition.
UPDATE: I’m not sure if you decided to switch back to Grub or still continue to use systemd-boot?