Browser Caching not working

I have been trying to extend the expiry dates of 4 cache types to the recommended expiry period of 8+ days but I get the following notification;

Browser Caching is not working properly:
– Your server may not have the “expires” module enabled (mod_expires for Apache, ngx_http_headers_module for NGINX)
– Another plugin may be interfering with the configuration
If re-checking and restarting does not resolve, please check with your host or open a support ticket with us.

I am having this problem identified by the Hummingbird plugin. My web host uses an Apache server and confirms that the “expires” module for NGINX is enabled. The website is fyzunt-games.international

Page Caching,Gravatar Caching and RSS Caching all work ok. Browser Caching, however, has 4 cache types currently disabled, which are Javascript, css, Media and Images. I have activation set as Automatic.

My Hummingbird performance test shows a drop from 88/100 to 73/100 over the past month. I have added no new plugins lately and deactivated WP-Optimise, as I thought there might be a conflict there. The theme, Twenty Fourteen, and all plugins are up to date.

Any suggestions to help resolve the issue would be greatly appreciated.