Inicialização dupla do Debian e CentOS UEFI - Não é possível carregar o Debian

Estou tentando instalar o Debian e o CentOS em um disco com uma inicialização UEFI. Quando o Debian inicializa, recebo o erro na imagem abaixo:

Para explicar como tentei configurar isso, mostrarei o que fiz com o particionamento. Abaixo está uma foto do meu particionamento inicial do Debian (observe que deixei algum espaço livre no final para colocar o ponto de montagem "/" do CentOS).

Depois que correu e instalou funcionou bem. Em seguida, coloquei uma unidade USB para inicializar e instalar o CentOS. Quando cheguei à tela de partição, era assim que parecia (antes de qualquer modificação):

Fiz então uma partição de 20GiB para o / do CentOS. Além disso, na seção de partição Debian, modifiquei a partição /boot/efi para ter o "ponto de montagem (veja a extrema direita da imagem)" de /boot/efi. Isso então parecia se duplicar na seção de partição do CentOS. O resultado é apresentado abaixo:

Ao inicializar, vejo duas opções, uma para CentOS e outra para Debian. Se eu selecionar CentOS, funciona bem. Se eu selecionar Debian, recebo o erro mostrado no primeiro link deste post. Minha pergunta é por quê?

Meu diretório EFI está abaixo.

[root@localhost EFI]# cd /boot/efi/EFI
[root@localhost EFI]# ls
BOOT  centos  debian
[root@localhost EFI]# ls centos debian
centos:
BOOT.CSV     fonts  fwupia32.efi  grub.cfg  grubx64.efi  MokManager.efi  shimx64-centos.efi
BOOTX64.CSV  fw     fwupx64.efi   grubenv   mmx64.efi    shim.efi        shimx64.efi

debian:
grubx64.efi

Meu /boot/efi/EFI/centos/grub.cfg está abaixo:

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub2-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
set pager=1

if [ -s $prefix/grubenv ]; then
  load_env
fi
if [ "${next_entry}" ] ; then
   set default="${next_entry}"
   set next_entry=
   save_env next_entry
   set boot_once=true
else
   set default="${saved_entry}"
fi

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
else
  menuentry_id_option=""
fi

export menuentry_id_option

if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function load_video {
  if [ x$feature_all_video_module = xy ]; then
    insmod all_video
  else
    insmod efi_gop
    insmod efi_uga
    insmod ieee1275_fb
    insmod vbe
    insmod vga
    insmod video_bochs
    insmod video_cirrus
  fi
}

terminal_output console
if [ x$feature_timeout_style = xy ] ; then
  set timeout_style=menu
  set timeout=5
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
  set timeout=5
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/00_tuned ###
set tuned_params=""
set tuned_initrd=""
### END /etc/grub.d/00_tuned ###

### BEGIN /etc/grub.d/01_users ###
if [ -f ${prefix}/user.cfg ]; then
  source ${prefix}/user.cfg
  if [ -n "${GRUB2_PASSWORD}" ]; then
    set superusers="root"
    export superusers
    password_pbkdf2 root ${GRUB2_PASSWORD}
  fi
fi
### END /etc/grub.d/01_users ###

### BEGIN /etc/grub.d/10_linux ###
menuentry 'CentOS Linux (3.10.0-957.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-957.el7.x86_64-advanced-4b9ca680-8e47-494f-8a98-991aab9d51e6' {
    load_video
    set gfxpayload=keep
    insmod gzio
    insmod part_gpt
    insmod xfs
    set root='hd0,gpt3'
    if [ x$feature_platform_search_hint = xy ]; then
      search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt3 --hint-efi=hd0,gpt3 --hint-baremetal=ahci0,gpt3  4b9ca680-8e47-494f-8a98-991aab9d51e6
    else
      search --no-floppy --fs-uuid --set=root 4b9ca680-8e47-494f-8a98-991aab9d51e6
    fi
    linuxefi /boot/vmlinuz-3.10.0-957.el7.x86_64 root=UUID=4b9ca680-8e47-494f-8a98-991aab9d51e6 ro crashkernel=auto rhgb quiet 
    initrdefi /boot/initramfs-3.10.0-957.el7.x86_64.img
}
menuentry 'CentOS Linux (0-rescue-6afd59629baf4fd295f2313dd51b9e9e) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-6afd59629baf4fd295f2313dd51b9e9e-advanced-4b9ca680-8e47-494f-8a98-991aab9d51e6' {
    load_video
    insmod gzio
    insmod part_gpt
    insmod xfs
    set root='hd0,gpt3'
    if [ x$feature_platform_search_hint = xy ]; then
      search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt3 --hint-efi=hd0,gpt3 --hint-baremetal=ahci0,gpt3  4b9ca680-8e47-494f-8a98-991aab9d51e6
    else
      search --no-floppy --fs-uuid --set=root 4b9ca680-8e47-494f-8a98-991aab9d51e6
    fi
    linuxefi /boot/vmlinuz-0-rescue-6afd59629baf4fd295f2313dd51b9e9e root=UUID=4b9ca680-8e47-494f-8a98-991aab9d51e6 ro crashkernel=auto rhgb quiet 
    initrdefi /boot/initramfs-0-rescue-6afd59629baf4fd295f2313dd51b9e9e.img
}
if [ "x$default" = 'CentOS Linux (3.10.0-957.el7.x86_64) 7 (Core)' ]; then default='Advanced options for CentOS Linux>CentOS Linux (3.10.0-957.el7.x86_64) 7 (Core)'; fi;
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_ppc_terminfo ###
### END /etc/grub.d/20_ppc_terminfo ###

### BEGIN /etc/grub.d/30_os-prober ###
menuentry 'Debian GNU/Linux (9.8) (on /dev/sda2)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-simple-9a0b0533-9320-45f1-9b3d-0860da8822be' {
    insmod part_gpt
    insmod ext2
    set root='hd0,gpt2'
    if [ x$feature_platform_search_hint = xy ]; then
      search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  9a0b0533-9320-45f1-9b3d-0860da8822be
    else
      search --no-floppy --fs-uuid --set=root 9a0b0533-9320-45f1-9b3d-0860da8822be
    fi
    linux /boot/vmlinuz-4.9.0-8-amd64 root=UUID=9a0b0533-9320-45f1-9b3d-0860da8822be ro quiet
    initrd /boot/initrd.img-4.9.0-8-amd64
}
submenu 'Advanced options for Debian GNU/Linux (9.8) (on /dev/sda2)' $menuentry_id_option 'osprober-gnulinux-advanced-9a0b0533-9320-45f1-9b3d-0860da8822be' {
    menuentry 'Debian GNU/Linux (on /dev/sda2)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-/boot/vmlinuz-4.9.0-8-amd64--9a0b0533-9320-45f1-9b3d-0860da8822be' {
        insmod part_gpt
        insmod ext2
        set root='hd0,gpt2'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  9a0b0533-9320-45f1-9b3d-0860da8822be
        else
          search --no-floppy --fs-uuid --set=root 9a0b0533-9320-45f1-9b3d-0860da8822be
        fi
        linux /boot/vmlinuz-4.9.0-8-amd64 root=UUID=9a0b0533-9320-45f1-9b3d-0860da8822be ro quiet
        initrd /boot/initrd.img-4.9.0-8-amd64
    }
    menuentry 'Debian GNU/Linux, with Linux 4.9.0-8-amd64 (on /dev/sda2)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-/boot/vmlinuz-4.9.0-8-amd64--9a0b0533-9320-45f1-9b3d-0860da8822be' {
        insmod part_gpt
        insmod ext2
        set root='hd0,gpt2'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  9a0b0533-9320-45f1-9b3d-0860da8822be
        else
          search --no-floppy --fs-uuid --set=root 9a0b0533-9320-45f1-9b3d-0860da8822be
        fi
        linux /boot/vmlinuz-4.9.0-8-amd64 root=UUID=9a0b0533-9320-45f1-9b3d-0860da8822be ro quiet
        initrd /boot/initrd.img-4.9.0-8-amd64
    }
    menuentry 'Debian GNU/Linux, with Linux 4.9.0-8-amd64 (recovery mode) (on /dev/sda2)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-/boot/vmlinuz-4.9.0-8-amd64-root=UUID=9a0b0533-9320-45f1-9b3d-0860da8822be ro single-9a0b0533-9320-45f1-9b3d-0860da8822be' {
        insmod part_gpt
        insmod ext2
        set root='hd0,gpt2'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  9a0b0533-9320-45f1-9b3d-0860da8822be
        else
          search --no-floppy --fs-uuid --set=root 9a0b0533-9320-45f1-9b3d-0860da8822be
        fi
        linux /boot/vmlinuz-4.9.0-8-amd64 root=UUID=9a0b0533-9320-45f1-9b3d-0860da8822be ro single
        initrd /boot/initrd.img-4.9.0-8-amd64
    }
}

### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

UPDATE - Got A Working Solution, but not happy how I got there (I would like to someone to tell me why my system ended up this way) : In my /boot/efi/EFI/centos/grub.cfg file I manually edited the lines under the Debian menu entry (or sub-menu entries) starting with the word "linux" or initrd" to the words "linuxefi" and "initrdefi" respectively. I can't understand why I've had to manually edit this grub file to make my debian system boot. I must be doing something very wrong right from the installation/setup stages of the operating systems for me to run into this problem. What is happening?