php SoapServer empty response with large data

Question

I'm struggling with a crazy behaviuor:

I want to send a response with SoapServer, but when the data gets too large i get an empty Response (tested with soapUI)

Response From Server:

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Encoding: gzip
Vary: Accept-Encoding
Date: Sat, 15 Apr 2017 00:54:26 GMT
Connection: close
Content-Length: 0

there is no error in the error-logs, the is no Timing-Problem

i built up a static Response for testing:

$array=(object) 
[
    (object)
    [
        'CallDirection' => 'Inbound',
        'CallHangUpDateTime' => "2017-04-11 11:11:11"
    ],
    (object)
    [
        'CallDirection' => 'Inbound',
        'CallHangUpDateTime' => "2017-04-11 11:11:11"
    ]
];

as soon as the Array gets more than 52 Elements (all the same for testing), the response is empty when the elements have more items, the amount of working elements is smaller (e.g. 31)

the Array will be returned in the following Code:

$test = new getDialerTimeLineCallsResult((object) 
    [
        'DialerOrderCallResults' => (object) $array,
        'ServiceResult' => (object) 
                            [
                                'ServiceCode' => 0,
                                'ServiceDuration' => 0,
                                'ServiceMessage' => "test",
                                'ServiceReference' => $ServiceReference,
                                'ServiceSuccess' => $result
                            ]
    ]);
$test = new SoapVar($test,SOAP_ENC_OBJECT, null, null, 'getDialerTimeLineCallsResult');
return $test;

i've written several steps to verify that $test in the end holds a soapvar, and it does!

but as soon as the result will get too large the response will be empty

i've checked that there are no Memory-Limitations, there is no error in the error-log, no Timing-Problem, tested on 2 Servers running PHP5.x, Windows and Linux, same result

Does anybody know why this is happening?