content-length has not appeared on HTML header response. I have added "content-length" in /clientheaders in dispatcher.any file as per documentation. Still, this does not appear in the header response for HTML.
/clientheaders is not for adding headers to response but to allow headers to pass to publisher iinstance from request.
Could you check if you have enabled caching html headers on dispatcher. If a request is being served from dispatcher and headers are not being cached, the response headers will miss the actual response headers.
To enable header caching, add /headers section to /cache section like