An error like the one below shows up in the Apache HTTP Server's error_log where AEM Dispatcher module is installed. /content/test.html is not a page that exists in your site.
[Mon Mar 12 21:10:08 2018] [error] [client 127.0.0.1] File does not exist: /opt/aem/dispatcher/cache/content/test.html, referrer: https://www.adobe.com/
AEM, Apache HTTP Server, Dispatcher
The dispatcher farm .any configuration /filter section doesn't allow dispatcher to process requests to /content/test.html so Apache HTTP Server takes over the request. The default handler of Apache attempts to process the request and sees that the file /opt/aem/dispatcher/cache/content/test.html doesn't exist.
It is a normal behavior of Apache HTTP Server so the error can be ignored.