I have same problem this case.
I think that. jetpack server didn’t support SNI(Server Name Indication) connect.
SNI makes be a lot of sites use to same 443 port.
also curl didn’t support SNI connect.
I tested curl call on same server.
curl -A "Jetpack by WordPress.com" -is -H 'Content-Type: text/xml' --data '<?xml version="1.0"?><methodCall><methodName>demo.sayHello</methodName><params></params></methodCall>' 'https://wp.enteroa.kr/xmlrpc.php?for=jetpack' && echo
then get this result.
HTTP/1.1 200 OK
Date: Sat, 12 Mar 2016 07:48:38 GMT
Server: Apache
Set-Cookie: session=;Max-Age=0;path=/
Connection: close
Cache-Control: max-age=2592000
Expires: Mon, 11 Apr 2016 07:48:38 GMT
Cache-Control: no-cache
Set-Cookie: session=;Max-Age=0;path=/
Strict-Transport-Security: max-age=86400
Content-Length: 435
Content-Type: text/xml; charset=UTF-8
However other server didn’t connecting it then result is empty. also access_log is empty.
i think SNI is not wrong setting. it’s modern technology.