index.js

const Vue = require('vue')
const renderer = require('vue-server-renderer').createRenderer()

// Class attributes with newlines in the for formatting end up rendering 
// trailing `\n` characters which causes the classname not to apply.  
// I.e., `long-classname-2 long-classname-3\n long-classname-4`
// So .long-classname-3 styles to not apply
const app = new Vue({
  template:
`<div>
    <p class="class-1 class-2 class-3">
        Working
    </p>
    <p class="long-classname-1 long-classname-2 long-classname-3
              long-classname-4 long-classname-5 long-classname-6">
        Broken
    </p>
</div>`,
})
renderer.renderToString(app, (err, html) => {
  if (err) throw err
  console.log(html)
})