Doesn't start with init.lua

Describe the bug When I use init.vim the preview starts as normal, and when I use init.lua nothing starts, with no errors.

To Reproduce

1. Install vim-plug and paq.nvim (sorry, apparently one can't use vim-plug with init.lua so I had to change when I rewrote it).

2. Take

" init.vim
set nocp
filetype plugin on
let g:NVIM_PLUGINS_DIR = stdpath('config') . '/plugged'
call plug#begin(NVIM_PLUGINS_DIR)
Plug 'iamcco/markdown-preview.nvim', { 'do': 'cd app && yarn install' }
call plug#end()

and

-- init.lua
vim.o.cp = false
vim.cmd("filetype plugin on")
require "paq" {
{"iamcco/markdown-preview.nvim", as="markdown-preview", run="cd app && yarn install" };
}

and install the plugin (with :PlugInstall for the first and :PaqInstall for the second).

3. Open some markdown file using nvim -u init.vim file.md. Run :MarkdownPreview. Works as expected (server starts at localhost, browser opens it).
4. Open the markdown file using nvim -u init.lua file.md. Run :MarkdownPreview. Nothing happens (and no errors). In particular, the server doesn't seem to have started (when I use the address I have when it works, I get "not found").

Expected behavior Everything works exactly the same for the two setups.

Desktop:

• OS: Mac OS X 10.14.6

Log:

checkhealth gives:

health#mkdp#check
========================================================================
  - INFO: Platform: macos
  - INFO: Nvim Version: NVIM v0.6.0-dev+9-g490615612
  - INFO: Node version: v16.4.2

  - INFO: Script: std('data')/site/pack/paqs/start/markdown-preview/app/server.js
  - INFO: Script exists: 1
  - OK: Using node

Otherwise the plugin has been working great, thanks for all your hard work!