title: Wordpress "Save Draft" fails: "the response is not a valid JSON response"
body: <p>I have this error every time I try to save my draft or publish or many other operations (and on all the news):</p>
  
  <pre><code>Updating failed. Error message: The response is not a valid JSON response.
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/MF44I.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MF44I.png" alt="Wordpress json not valid"></a></p>
  
  <p>Request:</p>
  
  <pre><code>{"id":488,"content":"&lt;!-- wp:paragraph --&gt;\n&lt;p&gt;Try &lt;/p&gt;\n&lt;!-- /wp:paragraph --&gt;","title":"Try"}
  </code></pre>
  
  <p>Response extract, looking at network tab (for some bizarre reason it includes html in addition to json):</p>
  
  <pre><code>&lt;span class="posted-on"&gt;Posted on
  ...
  &lt;/span&gt;{"id":488,"date":"2020-05-08T22:57:44","date_gmt":"2020-05-08T21:57:44","guid":{"rendered":
  ...
  </code></pre>
  
  <p>The solution used for other questions is to use the old <code>Classic Editor</code> but i prefear the new one:
  <a href="https://stackoverflow.com/questions/59009827/publishing-or-uploading-failed-error-message-the-response-is-not-a-valid-json">Publishing or uploading failed. Error message: &quot;The response is not a valid JSON response&quot;</a></p>