title: Magento 2 blank page but not empty
body: <p>I am developing a Magento 2.3 site which was working but has stopped. When I try to get a page up, I get a blank screen. Although it looks empty, it actually contains a little content:</p>
  
  <pre><code>  &lt;!doctype html&gt;
  &lt;html lang="en"&gt;
      &lt;head &gt;
                  &lt;meta charset="utf-8"/&gt;
  &lt;meta name="description" content="Blah Blah"/&gt;
  &lt;meta name="keywords" content="More blah blah"/&gt;
  &lt;meta name="robots" content="INDEX,FOLLOW"/&gt;
  &lt;title&gt;&lt;/title&gt;
  &lt;link  rel="icon" type="image/x-icon" href="http://www.magento2.domain/pub/media/favicon/stores/1/3-ladies-bg.jpg" /&gt;
  &lt;link  rel="shortcut icon" type="image/x-icon" href="http://www.magento2.domain/pub/media/favicon/stores/1/3-ladies-bg.jpg" /&gt;
  &lt;link href='https://fonts.googleapis.com/css?family=Prosto+One' rel='stylesheet' type='text/css' /&gt;
  &lt;!--xxxabb2c66c7681e8f658--&gt;
  &lt;!-- Global site tag (gtag.js) - Google Analytics --&gt;
  &lt;script async src="https://www.googletagmanager.com/gtag/js?id=UA-xxxx-1"&gt;&lt;/script&gt;
  &lt;script&gt;
    window.dataLayer = window.dataLayer || [];
    function gtag(){dataLayer.push(arguments);}
    gtag('js', new Date());
  
    gtag('config', 'UA-131267613-1');
  &lt;/script&gt;            &lt;/head&gt;
      &lt;body data-container="body" data-mage-init='{"loaderAjax": {}, "loader": { "icon": "http://www.magento2.domain/pub/static/version1551796553/frontend/_view/en_GB/images/loader-2.gif"}}' class="cms-index-index page-layout-1column"&gt;
              &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>If I look in the system log, I see the following errors:</p>
  
  <pre><code>[2019-04-30 21:24:48] main.INFO: Broken reference: the 'theme.active.editor' element cannot be added as child to 'after.body.start', because the latter doesn't exist [] []
  [2019-04-30 21:24:48] main.INFO: Broken reference: the 'logger' element cannot be added as child to 'after.body.start', because the latter doesn't exist [] []
  </code></pre>
  
  <p>I've enabled error logging but I get nothing. Can anyone help?</p>
  
  <p>Alternatively, can somebody point me to a good map (or similar) of how magento 2 builds a page so I can try and track down the error.</p>