Libtins TCP stream missing packet?

First of all, thanks for your patience. This issue may only be due to my lack of understanding as I am a complete beginner in PDU, ...

I am trying to do some TCP stream reassembling using libtins in order to measure some metrics. The issue is, libtins is not detecting any new Stream when I would expect one to be created.

Here is how I am configuring my Sniffer:

int main()
{
    SnifferConfiguration config;
    config.set_promisc_mode(true);
    config.set_filter("tcp");

    // Create our follower
    Tins::TCPIP::StreamFollower follower;

    // Set the callback for new streams. Note that this is a std::function, so you
    // could use std::bind and use a member function for this
    follower.new_stream_callback(&on_new_stream);

    // Now set up the termination callback. This will be called whenever a stream is
    // stopped being followed for some of the reasons explained above
    follower.stream_termination_callback(&on_stream_terminated);

    Sniffer sniffer("en0", config);

    // And start sniffing, forwarding all packets to our follower
    sniffer.sniff_loop([&](PDU &pdu) {
        std::cout << "Received packet:" << pdu.size() << std::endl;
        follower.process_packet(pdu);
        return true;
    });
}

And here is my new stream callback:

// New stream is seen
void on_new_stream(Stream &stream)
{
    std::cout << "New Stream: "
              << "client:" << stream.client_port() << " to " << stream.server_addr_v4().to_string() << ":" << stream.server_port() << std::endl;

    stream.client_data_callback(&on_client_data);
    stream.server_data_callback(&on_server_data);
}

By loading the Google homepage with the cache disabled, the console will log a lot of "packet received" with their respective size, but will not log anything related to the creation of a new stream.

I tested by keeping the program running and going through a lot of different websites and I sometimes get the stream-related logging, so I guess all the code is not incorrect?

Is there anything wrong with my code? Is there an easier way to get the size of my TCP stream reassembled?

Many thanks.