Javascript error occurs discontinuously

Hi everyone, I am developing with a Visual Studio 2015 an Asp.Net core MVC project and in one of the razor pages there is the following javascript code:

<script>
    document.addEventListener("DOMContentLoaded", init, false);

    var filterDiv = "";
    var filterArea = "";
    var filterDividerUp = "";
    var filters_string = "";
    var filter_number = 0;
    var fields_list = [];
    var selectArray = [];
    var import_id = @lastImportId;
    var managementTable = "";
    managementTable = "@managementTableName";
    //fields_list = new Array();
    fields_list = @Html.Raw(Json.Serialize(fieldsList));
    filters_string = @Html.Raw(Json.Serialize(filters));

    function init() {
        filterDiv = document.getElementById("filterDiv");
        filterArea = document.getElementById("filterArea");
        filterDividerUp = document.getElementById("filterDividerUp");

        initFilter();
    }

    function initFilter()
    {
        var filters = [];
        var filter_parts = [];
        var filter_values = [];

        var html = "<div class=\"row\">";
        html += "<div class=\"col-md-3\"></div>";
        html += "<div class=\"col-md-2\">";
        html += "<p>Field</p>";
        html += "</div>";
        html += "<div class=\"col-md-1\">";
        html += "<p style=\"text-align:center\">&nbsp;</p>";
        html += "</div>";
        html += "<div class=\"col-md-4\">";
        html += "<p>Value</p>";
        html += "</div>";
        html += "<div class=\"col-md-2\"></div>";
        html += "</div>";

        if(filters_string == ""){
            filters.length = 0;
        } else{
            filters = filters_string.split("|");
        }

        for (f = 0; f < filters.length; f++)
        {
            filter_number++;
            html += "<div class=\"row\">";
            filter_parts = filters[f].split("§");
            html += "<div class=\"col-md-3\"></div>";
            html += "<div class=\"col-md-2\">";
            html += "<select id=\"fieldsSelector" + filter_number + "\" name=\"fieldsSelector" + filter_number + "\" class=\"form-control\" data-width=\"auto\" onchange=\"getValuesList('fieldsSelector" + filter_number + "', 'valuesSelector" + filter_number + "', '')\">";
            for (fd = 0; fd < fields_list.length; fd++)
            {
                html += "<option id=\"option" + fd + "fieldsSelector" + filter_number + "\" value=\"" + fields_list[fd] + "\"" + (filter_parts[0] == fields_list[fd] ? " selected" : "") + ">" + fields_list[fd] + "</option>";
            }
            html += "</select>";
            html += "</div>";
            html += "<div class=\"col-md-1\">";
            html += "<p style=\"text-align:center\">=</p>";
            html += "</div>";
            //filter_values = filter_parts[1].split("::");
            //for(v = 0; v < filter_values.length; v++){
            //    html += filter_values[v] + (v == filter_values.length - 1 ? "" : "-");
            //}
            html += "<div class=\"col-md-4\">";
            html += "<select id=\"valuesSelector" + filter_number + "\" name=\"valuesSelector" + filter_number + "\" class=\"form-control\" data-width=\"auto\" onchange=\"setFilters('fieldsSelector" + filter_number + "', 'valuesSelector" + filter_number + "')\">";
            html += "<option id=\"option0valuesSelector" + filter_number + "\" value=\"" + filter_parts[1] + "\" selected>Please Select</option>";
            html += "</select>";
            html += "</div>";
            selectArray[f] = "fieldsSelector" + filter_number + "-" + "valuesSelector" + filter_number + "-" + filter_parts[1];
            html += "<div class=\"col-md-2\"></div>";
            html += "</div>";
        }
        filterArea.innerHTML = html;

        if(filter_number > 0){
            for(var s = 0; s < selectArray.length;  s++){
                var splitSelect = selectArray[s].split("-");
                getValuesList(splitSelect[0], splitSelect[1], splitSelect[2]);
            }
        }
    }

    function getValuesList(changingSelectorId, loadingSelectorId, selectedItem) {
        var selectedField = "";
        selectedField = $("#" + changingSelectorId).val();$.ajax({
            type: 'GET',
            dataType: 'json',
            contentType: 'application/json',
            url: '@Url.Action("GetData", "AjaxDatabaseManager")',
            data: { lookupTable : JSON.stringify(managementTable), lookupField : JSON.stringify(selectedField),
                importid : import_id},
            success: function (result) {
                var optionNumber = 1;

                var resultObj = result; //JSON.parse(result);

                $("#" + loadingSelectorId).empty(); // remove old options$("#" + loadingSelectorId).append("<option id=\"pleaseselect" + loadingSelectorId + "\" value=\"pleaseSelect\" " + (selectedItem == ""? "selected": "") + ">Please Select</option>");$.each(resultObj, function(key, val){$("#" + loadingSelectorId).append("<option id=\"option" + optionNumber + loadingSelectorId + "\" value=\"" + val + "\" " + (selectedItem != "" && val == selectedItem? "selected": "") + ">" + val + "</option>");
                    optionNumber++;
                });
            }
        });
    }</script>

Occasionally, after following the same steps in previous navigation if open the same page, the following errors occur:

Errore pagina web
-----------------
Errore: Errore non specificato.

Errore pagina web
-----------------
Errore: Impossibile recuperare la proprietà 'addEventListener' di un riferimento nullo o non definito

Errore pagina web
-----------------
Errore: Impossibile recuperare la proprietà 'createElement' di un riferimento nullo o non definito

Errore pagina web
-----------------
Errore: Bootstrap's JavaScript requires jQuery

Errore pagina web
-----------------
Errore: Impossibile recuperare la proprietà 'valHooks' di un riferimento nullo o non definito

Errore pagina web
-----------------
Errore: Impossibile recuperare la proprietà 'createElement' di un riferimento nullo o non definito

Errore pagina web
-----------------
Errore: Impossibile recuperare la proprietà 'createElement' di un riferimento nullo o non definito

Would you like to point to the javascript code what is wrong? I'm going crazy!

Thank you

Paolo