Synchrony not switching to Synchrony-proxy after configuration from documentation.

Summary

Set up Confluence with internal Synchrony proxy and Apache from official documentation page. 

Create new page or edit old one. Error message will be displayed "Unable to communicate with server. Saving is not possible at the moment.".

Specifying below setting inside server.xml, causes several JS files to point to wrong location on server.

proxyName="localhost" proxyPort="8090"

Environment

• CentOS Linux release 7.3.1611 (Core)
• Java 1.8.0_111
• Confluence 6.0.1,6.0.2,6.0.3
• Apache/2.4.6 (CentOS)

Steps to Reproduce

Follow the documentation for setting up Confluence server with internal synchrony proxy. And setup confluence - server.xml, confluence-home - confluence.cfg.xml and apache - apache.conf like this:

server.xml

<Server port="8000" shutdown="SHUTDOWN" debug="0">
    <Service name="Tomcat-Standalone">
        <Connector port="8090" connectionTimeout="20000" redirectPort="8443"
                maxThreads="48" minSpareThreads="10"
                enableLookups="false" acceptCount="10" debug="0" URIEncoding="UTF-8"
                protocol="org.apache.coyote.http11.Http11NioProtocol"/>
                proxyName="localhost" proxyPort="8090" />
...

confluence.cfg.xml

...
<property name="synchrony.proxy.enabled">true</property>
...

 
apache.conf

...
<VirtualHost *:80>
  ProxyRequests Off
  ProxyPreserveHost On

  RewriteEngine On
  RewriteCond %{REQUEST_URI} !^/synchrony
  RewriteRule ^/(.*) http://localhost:8090/synchrony-proxy/$1 [P]

  <Proxy *>
      Require all granted
  </Proxy>

ProxyPass /synchrony-proxy http://localhost:8090/synchrony-proxy

<Location /synchrony-proxy>
    Require all granted
    RewriteEngine on
    RewriteCond %{HTTP:UPGRADE} ^WebSocket$ [NC]
    RewriteCond %{HTTP:CONNECTION} Upgrade$ [NC]
    RewriteRule .* ws://localhost:8090%{REQUEST_URI} [P]  </Location>
</Location>

  ProxyPass / http://localhost:8090
  ProxyPassReverse / http://localhost:8090

  <Location />
      Require all granted
  </Location>
</VirtualHost>
...

Expected Results

With internal synchrony proxy set as per documentation, we can save changes in editor.

Actual Results

When trying to save page, error message is displayed: "Unable to communicate with server. Saving is not possible at the moment."

Logs are not showing errors (catalina, confluence or synchrony), only 404 in web browser inspect under network for several resources e.g:
http://localhost/synchrony/resources/js/vendor/sockjs.min.js
http://localhost/synchrony/resources/js/synchrony.min.js

Resources are available in these locations:
http://localhost/synchrony-proxy/resources/js/vendor/sockjs.min.js
http://localhost/synchrony-proxy/resources/js/synchrony.min.js
 
Workaround

If inside server.xml proxyName and proxyPort are removed, urls will change for resources mentioned in Actual Result from synchrony to synchrony-proxy, but then new problems will appear.
At this point there is no workaround.