SharePoint Rest API and Javascript Issue

I am using SharePoint 2013 Enterprise. I have 3 List. Now I am creating custom form which fully in jQuery and javascript.

From the 3 list, 2 list works as detail so I have two tables where we can add more than 1 record. At the time of saving record I am checking that this 2 list have attachment or not, if they don't have then I am deleting record and showing alert message. I don't have any error and when I debug it works smoothly as expected.

But issue is that when I run without debugging it does not show alert message.

Below code is my common code for adding record:

function CreateListItemWithDetails(listName, newItem) {
    return $.ajax({
        url: _spPageContextInfo.siteAbsoluteUrl + "/_api/web/lists/getbytitle('" + listName + "')/items",
        type: "POST",
        contentType: "application/json;odata=verbose",
        data: JSON.stringify(newItem),
        headers: {
            "Accept": "application/json;odata=verbose",
            "X-RequestDigest": $("#__REQUESTDIGEST").val()
        }
    });
}
function GetItemTypeForListName(name) {
    return "SP.Data." + name.charAt(0).toUpperCase() + name.split(" ").join("").slice(1) + "ListItem";
}
function getAttachments(listName, _Id) {
        return $.ajax({
            url: "/_api/web/lists/getbytitle('" + listName + "')/items(" + _Id + ")/AttachmentFiles",
            method: "GET",
            headers: { "Accept": "application/json; odata=verbose" }
        });
    }

This is my submit code, to make it short I will put main code only:

$("#btnSubmit").click(function () {
    var errMsg = "Following error occurd.\n", errCnt = 0;
            var listName = "GatePass";
            var itemType = GetItemTypeForListName(listName);
            var area = new Array();
            var newItem = {
                "__metadata": { "type": itemType },
                "Title": $("#txCompanyName").val(),
                "Area": area.join(", "),
                "FromDate": $("#fromDate").val(),
                "ToDate": $("#toDate").val(),
                "Approver": $("#approver").val(),
                "OtherOldBuildingArea": $("#txOldOtherAreas").val(),
                "OtherNewBuildingArea": $("#txNewOtherAreas").val()
            };
            CreateListItemWithDetails(listName, newItem).
                then(function (data) {
                    var gatePassID = data.d.ID;
                    $('#gatePass >tbody >tr').each(function (i, row) {
                        var $tds = $(this).find('td')
                        var updateItemGatePassDetails = {
                            "__metadata": { "type": GetItemTypeForListName("GatePassDetails") },
                            "GatePassIDId": gatePassID.toString()
                        };
                        getAttachments("GatePassDetails", $tds.eq(6).text())
                            .then(function (data) {
                                var attachments = data.d.results;
                                if (attachments.length == 0) {
                                    errCnt++;
                                    errMsg += errCnt.toString() + ". Missing civil id / passport document for " + $tds.eq(0).text() + "\n";
                                }
                            });
                        UpdateListItemWithDetails("GatePassDetails", updateItemGatePassDetails, $tds.eq(6).text());
                    });

                    $('#vehicle >tbody >tr').each(function (i, row) {
                        var $tds = $(this).find('td')
                        var updateItemGatePassVehicleDetails = {
                            "__metadata": { "type": GetItemTypeForListName("GatePassVehicleDetails") },
                            "GatePassIDId": gatePassID.toString()
                        };
                        getAttachments("GatePassVehicleDetails", $tds.eq(6).text())
                            .then(function (data) {
                                var attachments = data.d.results;
                                if (attachments.length == 0) {
                                    errCnt++;
                                    errMsg += errCnt.toString() + ". Missing vehicle document for " + $tds.eq(0).text() + "\n";
                                }
                            });
                        UpdateListItemWithDetails("GatePassVehicleDetails", updateItemGatePassVehicleDetails, $tds.eq(6).text());
                    });
                    if (errCnt > 0) {
                        DeleteListItemWithDetails(listName, gatePassID);
                        alert(errMsg);
                        return false;
                    }
                });
});