I have the following XLSX template:

When exporting, it results in:

Here’s the relevant part of my source code:

        var template = new XLTemplate(PropertiesFile.GetRequiredProperty(PropertiesFile.TEMPLATE_PATH));

        var dataShipments = new DataTable();
        dataShipments.Columns.Add("Column1", typeof(string));
        dataShipments.Columns.Add("Column2", typeof(string));
        ...
        dataShipments.Columns.Add("Column30", typeof(string));
        dataShipments.Columns.Add("Column31", typeof(string));
        dataShipments.Columns.Add("Column32", typeof(string));
        dataShipments.Columns.Add("Column33", typeof(string));


        IQueryable<IGrouping<string, DataItems>> groupItemsByColumn2 = dataItems.GroupBy(item => item.column2);

        foreach (IGrouping<string, DataItems> groupedItemByColumn2 in groupItemsByColumn2)
        {
            IList<DataItems> items = groupedItemByColumn2.ToList();
            foreach (DataItems item in items)
            {
                //Aquíe es donde se asignan los valores:
                DataRow newRow = dataShipments.NewRow();
                newRow["Column1"] = item.Column1 ?? string.Empty;
                newRow["Column2"] = item.Column2 ?? string.Empty;
                ...
                newRow["Column30"] = item.Column30 ?? string.Empty;
                newRow["Column31"] = item.Column31 ?? string.Empty;
                newRow["Column32"] = item.Column32 ?? string.Empty;
                newRow["Column33"] = item.Column33 ?? string.Empty;
                dataShipments.Rows.Add(newRow);
            }
        }

        template.AddVariable("item",dataShipments);

        //Lo siguiente parece que funciona bien debido a que se aplican todos los títulos:
        template.AddVariable("Column1Lbl", "Títlo 1");
        template.AddVariable("Column2Lbl", "Títlo 2");
        ...
        template.AddVariable("Column30Lbl", "Títlo 30");
        template.AddVariable("Column31Lbl", "Títlo 31");
        template.AddVariable("Column32Lbl", "Títlo 32");
        template.AddVariable("Column33Lbl", "Títlo 33");

        template.Generate();

Interestingly, if I swap Column 30 with Column 32 by copying and pasting, it results in:

Note that the titles are processed correctly.