worksheet.save(),it stay locked

Question

I have developed a windows form project that is export large date in excel. Sometimes worksheet.save() method takes 1 hour or infitine time. I think it stay locked, but I don't know why. Does anyone have any ideas to solve this?

    ...
    FileInfo temp_excel_file = new FileInfo(Path.Combine(ConfigFile.ConfigsPaths["ExcelRaporFolder"], "temp", "Rakip.xlsm"));
    rapor_file = new FileInfo(Path.Combine(ConfigFile.ConfigsPaths["ExcelRaporFolder"], "excel", FileName + ".xlsm"));
    File.Copy(temp_excel_file.FullName, rapor_file.FullName);
    Log.LogYaz(rapor_file.Name + "-Excell Açılıyor..");
    SpreadsheetDocument myDoc = SpreadsheetDocument.Open(rapor_file.FullName, true);
    IEnumerable<Sheet> sheets = myDoc.WorkbookPart.Workbook.Descendants<Sheet>();
    WorksheetPart worksheetPart = (WorksheetPart)myDoc.WorkbookPart.GetPartById(sheets.Skip(1).First().Id);
    SheetData sheetData = worksheetPart.Worksheet.Elements<SheetData>().First();
    Log.LogYaz(rapor_file.Name + "-Rowlar Yaziliyor..");
    uint row = 2;
    Stopwatch swLoadTime = new Stopwatch();
    swLoadTime.Start();
    foreach (var row_index in filtered_data)
    {
    ....
       sheetData.AppendChild(Utils.CreateRow(row, 0, cell_data));
       row++;
    }
    swLoadTime.Stop();
    string loadRowTime = swLoadTime.Elapsed.ToString();
    Log.LogYaz("RowsWasLoaded -" + FileName.ToString() + Environment.NewLine + "  Load Row Time:" + loadRowTime);
    swLoadTime.Reset();
    swLoadTime.Start();
    worksheetPart.Worksheet.Save();
    myDoc.Close();
    myDoc = null;
    swLoadTime.Stop();
    Log.LogYaz("RaporYazildi -" + FileName.ToString() + Environment.NewLine + "  Load Row Time:" + loadRowTime + Environment.NewLine + "  Save File Time:" + swLoadTime.Elapsed);