Modal scroll body don’t work after second calling ajax content

I have a modal in Boostrap 4. I put <div class="modal-dialog modal-lg modal-dialog-scrollable">

I don’t know why when I choose from dropdown second time, body from modal is not scrolling, in console I don’t have any error!

I made an gif with how it works Gif movie with action

I call via ajax and display content in to modal. This is js code that I use:

$(document).ready(function(e) {
    $('.select2bs4').select2({
        theme: 'bootstrap4'
    })
    $('#map_cat').on('change', function() {
        var cat = $("#map_cat option:selected").val();
        $.ajax({
            url: "products/categories/get_char_category",
            type: "POST",
            data: {
                cat_id: cat,
                [csrf_name]: csrf_value
            },
            dataType: "json",
            beforeSend: function() {
                $("#loaderDiv").show();
                $('#characteristics').empty();
                $('#text-inf').empty();
            },
            success: function(data) {

                $("#loaderDiv").hide();
                $('#characteristics').empty();
                $('#text-inf').empty();

                var textInf = '<div class="mb-4 text-center"><?php echo $this->lang->line('match_char '); ?></div>';
                $('#text-inf').append(textInf);
                var mandatory = '';

                $.each(data, function(key, value) {
                    var mandatory = '';

                    if (value.name !== null) {

                        if (value.required !== null) {

                            var mandatory = 'mandatory';
                        }

                        var dataHtml = '<div class="col-md-12 form-group"><div class="row d-flex justify-content-between align-items-center"><div class="col-sm-6"><label class="' + mandatory + '"> ' + value.name + ' </label></div><div class="col-sm-6"><div><select name="char_id[]" class="form-control select2bs4"><option value="0"><?php echo $this->lang->line("char_select"); ?></option><?php foreach($chars as $cha){ ?><option value="<?php echo $cha->id; ?>"><?php echo $cha->char; ?></option><?php } ?></select></div></div></div></div>';
                        $('#characteristics').append(dataHtml);

                        $('.select2bs4').select2({
                            theme: 'bootstrap4'
                        })
                    }
                });
            },
            error: function(xhr, textStatus, errorThrown) {
                return false;
            }
        });
    });
});