QAbstractSocket::UnsupportedSocketOperationError with QSslSocket

Question

QAbstractSocket throws UnsupportedSocketOperationError when connecting to a host over QSslSocket::connectToHostEncrypted(),

Environnement: Qt 5.9.3 Ubuntu 16.04 (virtual machine) also Qt 5.9.3 Fedora 26 (native)

_socket = new QSslSocket{this};
connect(_socket, static_cast<void(QAbstractSocket::*) QAbstractSocket::SocketError) (&QAbstractSocket::error), this, &EventResource::streamError);

_socket->connectToHostEncrypted(_device->addressUrl().host(), 443, QSslSocket::ReadWrite, QSslSocket::IPv4Protocol);

void EventResource::streamError(QAbstractSocket::SocketError error)
{
    QDebug() << "Event error: " << error; 
    //QAbstractSocket::UnsupportedSocketOperationError
}

Can you please help me?
I don't understand the error and why it is happening?