Keep alive enabled but no for webpagetest

[robzilla]

You can use your browser's developer tools to inspect the HTTP headers. In your WPT results, you can click through to "Details" page and then click on any of the resources to view the request and response headers. I've attached an example.

Patrick's comments in this thread are relevant:

Quote:That means keep--alives are not really enabled. I'm partially convinced that hosting providers were doing that just so you thought it might be while still allowing them to disable it but when the browser sees that "close" it will close the connection.

The keep-alives are generally controlled at the server level and not controllable in .htaccess. You'll need to reach out to your hosting provider.

His suspicion is probably valid in your case.