SoapClient not rendering correct xml from SimpleXMLObject

We have an application that builds a correct XML request in SimpleXML. When outputting this with $element->asXml() I also get the correct XML. However when passing the SimpleXML object to the soapclient it will stripp all keys in array's.

I have tried several ways to fix this. Assigning keys to the elements. Several Soapclient features, and turning everything into an array. No result.

This is a abstract version of what i'm trying to achieve.

 $populate = new SimpleXMLElement('<Populate/>');
        $data = $populate->addChild('data');
        $roleKeysElement = $data->addChild('RoleKeys');
        $roleKeysElement->addChild('Operation', $settings[PopulateSettings::ROLE_KEYS] ?? Operations::MIRROR);

        $roleKeyElement1 = $roleKeysElement->addChild('RoleKey');
        $keyElement1 = $roleKeyElement1->addChild('Key');
        $certificateElement = 1->addChild('Certificate');
        $certificateElement->addChild('ValidUntil', 1);
        $certificateElement->addChild('Password', 2);
        $certificateElement->addChild('Thumbprint', 3);
        $certificateElement->addChild('Serial', 4);
        $certificateElement->addChild('Base64Data', 5);

        $roleKeyElement2 = $roleKeysElement->addChild('RoleKey');
        $keyElement2 = $roleKeyElement2->addChild('Key');
        $certificateElement = $keyElement2->addChild('Certificate');
        $certificateElement->addChild('ValidUntil', 1);
        $certificateElement->addChild('Password', 2);
        $certificateElement->addChild('Thumbprint', 3);
        $certificateElement->addChild('Serial', 4);
        $certificateElement->addChild('Base64Data', 5);

$response = $this->client->populate($populate);

My WSDL has maxOccurence=Unbound for certifcate in this case. But only 1 certifcate object is send. Only the first one.

What im getting from the simpleXML asXml() function is

<Populate>
    <data>
        <RoleKeys>
            <Operation>
                Mirror
            </Operation>
            <RoleKey>
                <Key>
                    <Certificate>
                        <ValidUntil>
                            1
                        </ValidUntil>
                        <Password>
                            2
                        </Password>
                        <Thumbprint>
                            3
                        </Thumbprint>
                        <Serial>
                            4
                        </Serial>
                        <Base64Data>
                            5
                        </Base64Data>
                    </Certificate>
                </Key>
            </RoleKey>
            <RoleKey>
                <Key>
                    <Certificate>
                        <ValidUntil>
                            1
                        </ValidUntil>
                        <Password>
                            2
                        </Password>
                        <Thumbprint>
                            3
                        </Thumbprint>
                        <Serial>
                            4
                        </Serial>
                        <Base64Data>
                            5
                        </Base64Data>
                    </Certificate>
                </Key>
            </RoleKey>
        </RoleKeys>
    </data>
</Populate>

This is correct

How ever the soap clients sends

<Populate>
    <data>
        <RoleKeys>
            <Operation>
                Mirror
            </Operation>
            <RoleKey>
                <Key>
                    <Certificate>
                        <ValidUntil>
                            1
                        </ValidUntil>
                        <Password>
                            2
                        </Password>
                        <Thumbprint>
                            3
                        </Thumbprint>
                        <Serial>
                            4
                        </Serial>
                        <Base64Data>
                            5
                        </Base64Data>
                    </Certificate>
                </Key>
            </RoleKey>
        </RoleKeys>
    </data>
</Populate>

To give a little more context here is the WSDL part of this request

<complexType name="KeyType">
    <sequence>
        <element minOccurs="0" maxOccurs="1" name="KeyUnlocks" type="s:string" />
        <choice minOccurs="1" maxOccurs="1">
            <element minOccurs="0" maxOccurs="1" name="Credentials">
                <complexType>
                    <sequence>
                        <element minOccurs="0" maxOccurs="1" name="Username" type="s:string" />
                        <element minOccurs="0" maxOccurs="1" name="Password" type="s:string" />
                    </sequence>
                </complexType>
            </element>
            <element minOccurs="0" maxOccurs="1" name="Certificate">
                <complexType>
                    <sequence>
                        <element minOccurs="1" maxOccurs="1" name="ValidUntil" type="s:dateTime" />
                        <element minOccurs="0" maxOccurs="1" name="Password" type="s:string" />
                        <element minOccurs="0" maxOccurs="1" name="Thumbprint" type="s:string" />
                        <element minOccurs="0" maxOccurs="1" name="Serial" type="s:string" />
                        <element minOccurs="0" maxOccurs="1" name="Base64Data" type="s:base64Binary" />
                    </sequence>
                </complexType>
            </element>
        </choice>
    </sequence>
</complexType>

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