API returning XML with no content

API returning XML with no content

I'm getting responses from the API with no content in the XML e.g.:

HTTP/1.1 200 OK
Server: ZGS
Date: Mon, 18 Aug 2014 06:56:35 GMT
Content-Type: text/xml;charset=utf-8
Content-Length: 124
Connection: close
Set-Cookie: bba2ee81f8=21d3ec82a550e42d7e34605b46da3dd9; Path=/
Set-Cookie: JSESSIONID=C4DF99BB8F5F93C0CDC3B14103897FF7; Path=/crm
X-XSS-Protection: 1
Set-Cookie: crmcsr=3e8ab997-21a2-4f61-9680-6abefbdc908c; Path=/; Secure
Pragma: no-cache
Cache-Control: no-cache
Expires: Thu, 01 Jan 1970 00:00:00 GMT
Strict-Transport-Security: max-age=15768000

<?xml version="1.0" encoding="UTF-8" ?>
<response uri="/crm/private/xml/Leads/insertRecords"><result></result></response>

As you can see, there's no error so I'm not sure how to debug it. This has just suddenly started today, not sure if it's a problem on my end or not.

Any ideas?