When wordpress is configured in a master-slave configuration, you need to be aware that making changes on the /wp-admin panel may not be saving the changes.
If you visit example.com/wp-admin you may be visiting the slave server. If you make changes on the slave server then lsync can simply overwrite the changes made.
You will

<IfDefine SLAVE>

  RewriteEngine On

  ProxyPreserveHost On

  ProxyPass /wp-admin/ http://${MASTER_SERVER}/wp-admin/
  ProxyPassReverse /wp-admin/ http://${MASTER_SERVER}/wp-admin/

  RewriteCond %{REQUEST_METHOD} =POST
  RewriteRule . http://${MASTER_SERVER}%{REQUEST_URI} [P]

</IfDefine>