Syntastic not working with local eslint

Question

I have a scenario where I have a local .eslintrc and the local eslint package installed. However, I notice that it does not populate a loclist on a file called app.js when I open the file and when I run :SyntasticCheck.

I have included the Syntastic config below. The complete .vimrc is hosted on github for more info.

I can confirm that ./node_modules/.bin/eslint app.js works as expected. The output from :SyntasticInfo:

Syntastic version: 3.8.0-26 (Vim 704, Linux, GUI)                                                                                                                                                           
Info for filetype: javascript.jsx                                                                                                                                                                           
Global mode: active                                                                                                                                                                                         
Filetype javascript.jsx is active                                                                                                                                                                           
The current file will be checked automatically                                                                                                                                                              
Available checkers: -                                                                                                                                                                                       
Currently enabled checkers: -

This is my Syntastic config:

let g:syntastic_always_populate_loc_list = 1
let g:syntastic_auto_loc_list = 1
let g:syntastic_check_on_open = 1
let g:syntastic_check_on_wq = 0 "skip checking on save and exit
"use locally installed version of eslint with syntastic, extracted from mtscout6/syntastic-local-eslint.vim
let s:lcd = fnameescape(getcwd())
silent! exec "lcd" expand('%:p:h')
let s:eslint_path = system('PATH=$(npm bin):$PATH && which eslint')
exec "lcd" s:lcd
let b:syntastic_javascript_eslint_exec = substitute(s:eslint_path, '^\n*\s*\(.\{-}\)\n*\s*$', '\1', '')
let g:syntastic_javascript_flowtype_exe = 'flow'
let g:syntastic_javascript_checkers = ['eslint', 'flow']

"aggregate errors from all checkers for a file type
let g:syntastic_aggregate_errors = 1
"automatically open and close error list when an error is detected
let g:syntastic_always_populate_loc_list = 1

"add rubocop to syntastic as a ruby checker
let g:syntastic_ruby_checkers = ['mri','rubocop']

"check if a file exists
function! HasConfig(file, dir)
  return findfile(a:file,escape(a:dir,' ') . ';') !=# ''
endfunction

" Merge commands into augroup vimrc
augroup vimrc
  "checks for .eslintrc and .jshintrc before falling back to standard
  autocmd BufNewFile,BufReadPre *.js  let b:syntastic_checkers =
    \ HasConfig('.eslintrc', expand('<amatch>:h')) ? ['eslint'] :
    \ HasConfig('.jshintrc', expand('<amatch>:h')) ? ['jshint'] :
    \     ['standard']

augroup end

" Typescript syntax checking using tsuqoyami
let g:tsuqoyami_disable_quickfix = 1
let g:syntastic_typescript_checkers = ['tslint', 'tsuquyomi']