Symptoms

When browsing the HTML documentation produced using HelpNDoc's default responsive template, the table of contents is empty, shows an infinite loading animation or an error message.

Solutions

First of all, make sure that the documentation is correctly browsed from a web server. See: The HTML documentation is not loading or behaving incorrectly  
Some web servers such as older versions of Microsoft IIS or Amazon S3 must be configured to return the correct mime type for JSON, WOFF and WOFF2 files. Requesting such files will have the following results:

In any case, we recommend that you web server is correctly configured to return the correct mime type for those files. Here is how this can be done for some servers:

Microsoft IIS

Edit your web.config file and add the following content:

<system.webServer>
    <staticContent>
        <mimeMap fileExtension=".json" mimeType="application/json" />
        <mimeMap fileExtension=".woff" mimeType="application/font-woff" />
        <mimeMap fileExtension=".woff2" mimeType="application/font-woff2" />
    </staticContent>
</system.webServer>

Amazon S3

Specify the property Content-Type property for every JSON, WOFF, and WOFF2 files. See Amazon S3 documentation: https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPUT.html