I have been stuck on this for several days now. The theme customizer does not apply any change, and the problem seems to be different from everything I've seen on online forums (lucky me).
The page customize.php loads fine, no error whatsoever is thrown and the Preview Panel is displayed properly. I have checked the responses of the Ajax calls, using the developer tools of browsers. I have set Apache logging to debug level, I have also activated logging at the Wordpress level and increased logging at the PHP level, but no error message whatsoever is present in the logs. And the Ajax requests sent by customize.php all get a success response.
However, when trying to edit ANY theme, both the default ones, and downloaded ones, while the preview panel is properly loaded, and while the preview panel shows the fading animation indicating that the preview panel is being refreshed to display the changes as I am typing modifications, no change is actually shown on the preview panel. Even clicking on the Save/Publish button does not apply the changes. No change is applied on the live website either. And all modification entered on the left-side editor are lost upon refresh of the page.
However, articles, and content can be created without problem from other parts of the admin panel. Settings can be changed, themes and plugins can be installed, and all sorts of write operations can be done without problem.
I have checked that the URL of the wordpress website is the same than the url of the wordpress directory in Wordpress Settings, as suggested in forums. I have tried to switch back and forth between themes hoping that the issue would magically go away as suggested in forums. I have also tried disabling all plugins and have even reinstalled wordpress from scratch. But the issue is still there, and the most frustrating is that no error is thrown anywhere, it just fails silently, so I'm here trying to guess.
I have checked file system permissions but all files and folders are owned by the correct apache user. I thought that maybe requests were being silently "cleaned" by a filter, but mod_security is not installed anywhere in the pipeline.
Our setup is as follow, even though I do not think it should relevant: we have one front-end apache server acting as a reverse proxy for another Apache Instance running wordpress on a different virtual machine not directly exposed to the internet (for various security policy reasons). I will post the HTTPD configuration files in a minute.
On the front-end Apache (ie. the reverse-proxy, which is the SSL termination point. Just mentioning it for context since I am not sure where to look at, but there is no problem whatseover with SSL so normally this should be irrelevant)
<VirtualHost *:443>
ServerName mywebsite.com
ServerAlias www.mywebsite.com
ProxyPass "/" "http://192.168.185.12:80/"
ProxyPassReverse "/" "http://192.168.185.12:80/"
ProxyPreserveHost On
CustomLog /var/log/mywebsite.com-access.log combined
ErrorLog /var/log/mywebsite.com-error.log
SSLCertificateFile /path/to/certicate
SSLCertificateKeyFile /path/to/private/key
</VirtualHost>
<VirtualHost *:80>
ServerName mywebsite.com
ServerAlias www.mywebsite.com
Redirect / https://mywebsite.com/
</VirtualHost>
On the Wordpress' Apache instance (ie. the backend)
<FilesMatch "\.php$">
SetHandler application/x-httpd-php
</FilesMatch>
<FilesMatch "\.phps$">
SetHandler application/x-httpd-php-source
</FilesMatch>
<VirtualHost *:80>
ServerName mywebsite.com
ServerAlias www.mywebsite.com
DocumentRoot /usr/local/www/wordpress
SetEnv HTTPS On
LogLevel debug
</VirtualHost>
<Directory /usr/local/www/wordpress>
AllowOverride All
Options -Indexes +FollowSymLinks
Order Allow,Deny
Allow from all
# For Apache 2.4 add:
Require all granted
</Directory>
<Location / >
ExpiresActive On
ExpiresDefault "now"
</Location>
Any clue, pointer or idea would be greatly appreciated.
Thanks
