title: "NodeAlreadySaved " error when using djangocms publishing page changes
body: <p><strong>Encounter an error when using djangocms publishing page changes.</strong></p>
  <p>when I ran <code>tail -f /var/log/apache2/error.log</code>, it returned:</p>
  <pre><code>treebeard.exceptions.NodeAlreadySaved: Attempted to add a tree node that is already in the database, referer: http://47.95.254.172/?edit
  </code></pre>
  <p>And when I allowed the settings.py DEBUG= True and click the 'Publish page changes' button:</p>
  <pre><code>NodeAlreadySaved at /admin/cms/page/1/en/publish/
  Attempted to add a tree node that is already in the database
  Request Method: POST
  Request URL:    http://47.95.254.172/admin/cms/page/1/en/publish/
  Django Version: 3.1.7
  Exception Type: NodeAlreadySaved
  Exception Value:    Attempted to add a tree node that is already in the database
  Exception Location: /root/env1/lib/python3.8/site-packages/treebeard/mp_tree.py, line 326, in process
  Python Executable:  /root/env1//bin/python
  Python Version: 3.8.5
  
  </code></pre>
  <p>I have run <code>python manage.py cms fix-tree</code> but it did not work. While <code>python manage.py cms check</code> returned <strong>10 checks successful!</strong>.</p>
  <p>I deployed the djangocms project with:</p>
  <p>apache2.4.41</p>
  <p>mod-wsgi 4.8.0</p>
  <p>django 3.1.7</p>
  <p>django-cms 3.8.0</p>
  <p>The python version in venv is 3.8.5, and mod-wsgi was compiled by python3.8.5 in the venv.</p>
  <p>Thank you for the help!</p>