gsl::span returned by function has wrong bytes

I have a function parsing a ZeroMQ multipart message and filling a struct containing a gsl::span<uint8_t>:

struct ProtocolMessage{
    ProtocolMessage() {}
    ProtocolMessage(std::initializer_list<std::string> headers): 
        headers{headers} {}
    ProtocolMessage(std::initializer_list<std::string> headers, gsl::span<uint8_t> body): 
        headers{headers}, body{body} {}
    ~ProtocolMessage() = default;

    std::vector<std::string> headers;
    gsl::span<uint8_t> body;
};

ProtocolMessage ProtocolAsts1::parseForwarderToClient(zmq::multipart_t&& msg) const {
    ProtocolMessage parsed;
    parsed.headers.push_back(msg.popstr());
    auto body = msg.pop();

    parsed.body = gsl::span<uint8_t>{body.data<uint8_t>(), body.size()};

    std::cout << "parseForwarderToClient" << std::endl;
        for(size_t i = 0; i < parsed.body.size(); ++i)
    std::cout << std::hex << std::setw(2) << std::setfill('0') << static_cast<short>(parsed.body.data()[i]);
    std::cout << std::dec << std::endl;
    return parsed;
}

The function calling this method does the following:

zmq::multipart_t msg{socketForwarder};
std::cout << msg.str();

auto parsed = parser->parseForwarderToClient(std::move(msg));

std::cout << "doLoop" << std::endl;
for(size_t i = 0; i < parsed.body.size(); ++i)
    std::cout << std::hex << std::setw(2) << std::setfill('0') << static_cast<short>(parsed.body.data()[i]);
std::cout << std::dec << std::endl;

The problem is that bytes printed with msg.str() and inside parseForwarderToClient are the same, while the ones printed in calling funciton are different (and then my code crash).

What am I doing wrong in this code (I am still a newbie in C++11/14 and gsl features)?