Autocomplete shows only one result

I'm working with an autocomplete but it only shows me one result in the dropdown.

The JSON format is like this:

"Registro": [
    {
        "attributes": {
            "codigo": "000427",
            "nodeValue": ""
        },
        "AR_DENO": "Aluminio",
        "AR_LER": "200140",
        "AR_PVP": {

        }
    },
    {
        "attributes": {
            "codigo": "000687",
            "nodeValue": ""
        },
        "AR_DENO": "Viruta de Aluminio",
        "AR_LER": "200140",
        "AR_PVP": {

        }
    }

the code is as follows:

    <script type="text/javascript">
    $(document).ready(function () {

        $(document).on('keydown', '.nombre', function () {

            var id = this.id;
            var splitid = id.split('_');
            var index = splitid[1];

            $('#' + id).autocomplete({
                source: function (request, response) {
                    $.ajax({
                        url: "articulosXMLjson.php?empresa=acme&familias=01?02?03?04?05?06?07?08?080?13?21",
                        type: 'get',
                        dataType: "json",
                        data: {
                            search: request.term
                        },

                        success: function (data) {
                            console.log(data);
                            response($.map(data, function (item) {
                                return {
                                    label: data["Registro"][0].AR_DENO +
                                        " " + data["Registro"][0].AR_LER,
                                    ler: data["Registro"][0].AR_LER,
                                    pvp: data["Registro"][0].AR_PVP,
                                    value: data["Registro"][0]["attributes"].codigo
                                };
                            }));
                        },
                        error: function (XMLHttpRequest, textStatus, errorThrown) {
                            alert(textStatus + " " + errorThrown);
                        }
                    });
                },
                select: function (event, ui) {

                    $(this).val(ui.item.label); // display the selected text                    
                    var codigo = ui.item.value; // selected id to input

                    // AJAX
                    $.ajax({
                        url: 'articulosXMLjson.php?empresa=acme&familias=01?02?03?04?05?06?07?08?080?13?21',
                        type: 'get',
                        data: {
                            codigo: codigo
                        },
                        dataType: 'json',

                        success: function (response) {
                            console.log(response);

                            var id = ui.item.value;
                            var nombre = ui.item.label;
                            var ler = ui.item.ler;
                            document.getElementById('ler_' + index).value = ler;
                        }
                    });
                    return false;
                }
            });
        });

        // Add more
        $('#addmore').click(function () {

            // Get last id 
            var nombre_id = $('.tr_input input[type=text]:nth-child(1)').last().attr('id');
            var split_id = nombre_id.split('_');

            // New index
            var index = Number(split_id[1]) + 1;

            // Create row with input elements
            var html = "<tr class='tr_input'><td><input type='text' class='nombre' id='nombre_" + index +
                "' placeholder='Nombre Artículo'></td><td><input type='text' class='ler' id='ler_" +
                index + "' ></td></tr>";

            // Append data
            $('tbody').append(html);

        });
    });
</script>

<input type='button' value='Añadir linea' id='addmore'>
<table border='1' style='border-collapse: collapse;'>
    <thead>
        <tr>
            <th>Nombre Artículo</th>
            <th>LER</th>
        </tr>
    </thead>
    <tbody>
        <tr class='tr_input'>
            <td>
                <input type='text' class='nombre' id='nombre_1' placeholder='Nombre artículo'>
            </td>
            <td>
                <input type='text' class='ler' id='ler_1'>
            </td>

        </tr>
    </tbody>
</table>