`:LeaderGuide` not works for nmap/nnoremap mappings

[yuntan]

Environment

vim-leader-guide: 8dff63fcc29811bb30fccb135f31ad488a9a6170 VIM 8.1

How to reproduce

minimal .vimrc

set rtp+=~/.vim/plugged/vim-leader-guide

syntax on
filetype plugin indent on

let mapleader = "\<Space>"
nnoremap <silent> <Leader> :<C-U>LeaderGuide '<Space>'<CR>

map <Leader>a :echo 'a'<CR>
nmap <Leader>b :echo 'b'<CR>
noremap <Leader>c :echo 'c'<CR>
nnoremap <Leader>d :echo 'd'<CR>

Open vim -N -u .vimrc. Press <Space>. I expected 4 key mappings are listed, but I got only 2 mappings.