Issue:
The combination of mxw/vim-jsx and junegunn/rainbow_parentheses.vim, with a custom g:rainbow#pairs list, breaks syntax highlighting.
Minimal .vimrc to replicate:
set nocompatible
filetype indent plugin on
syntax on
call plug#begin($VIM_PLUGINS_DIR)
Plug 'pangloss/vim-javascript'
Plug 'mxw/vim-jsx'
Plug 'junegunn/rainbow_parentheses.vim' " Breaks highlighting for template
call plug#end()
let g:jsx_ext_required = 0
let g:rainbow#pairs = [['(', ')'], ['[', ']'], ['{', '}'], ['<', '>']]
and then call the command :RainbowParentheses after, to toggle.
Temporary Solution
Disable the custom g:rainbow#pairs line.