Vim window become blank after resize when which-key is active

• OS: Ubuntu 18.04

• Vim: Neovim 0.3.1

If you think it's a bug, please provide a minimal vimrc to reproduce:

call plug#begin('~/.config/nvim/plugged')
Plug 'liuchengxu/vim-which-key', { 'on': ['WhichKey', 'WhichKey!'] }
call plug#end()

let mapleader = ' '
let maplocalleader = '\'

augroup vimrc
  autocmd!
  autocmd! User vim-which-key call which_key#register('<Space>', 'g:which_key_map')
  autocmd! FileType which_key
  autocmd  FileType which_key set laststatus=0
    \| autocmd BufLeave <buffer> set laststatus=2
augroup END

" ----------------------------------------------------------------------------
" vim-which-key
" ----------------------------------------------------------------------------
nnoremap <silent> <leader>      :<c-u>WhichKey '<Space>'<CR>
vnoremap <silent> <leader>      :<c-u>WhichKeyVisual '<Space>'<CR>
nnoremap <silent> <localleader> :<c-u>WhichKey '\'<CR>
let g:which_key_map = {}
let g:which_key_map.2 = 'which_key_ignore'
let g:which_key_map.3 = 'which_key_ignore'
let g:which_key_map.4 = 'which_key_ignore'
let g:which_key_map.5 = 'which_key_ignore'
let g:which_key_map.6 = 'which_key_ignore'
let g:which_key_map.7 = 'which_key_ignore'
let g:which_key_map.8 = 'which_key_ignore'
let g:which_key_map.9 = 'which_key_ignore'
let g:which_key_map.b = {
      \ 'name' : '+buffer' ,
      \ '1' : ['b1'        , 'buffer 1']        ,
      \ '2' : ['b2'        , 'buffer 2']        ,
      \ 'd' : ['bd'        , 'delete-buffer']   ,
      \ 'f' : ['bfirst'    , 'first-buffer']    ,
      \ 'h' : ['Startify'  , 'home-buffer']     ,
      \ 'l' : ['blast'     , 'last-buffer']     ,
      \ 'n' : ['bnext'     , 'next-buffer']     ,
      \ 'p' : ['bprevious' , 'previous-buffer'] ,
      \ '?' : ['Buffers'   , 'fzf-buffer']      ,
      \ }

Problem Description

If I press <Space> to active which-key, then resize neovim pane size in tmux, the neovim pane become blank until I press <ESC> to quit which-key or complete some mapping in which-key table.