Thanks for using Aspose APIs.
We were able to observe this issue as per your description with most recent version and logged it in our database for investigation and for a fix.
This issue has been logged as
CELLSNET-45571 - Default grey cell borders converted into dotted lines
Workbook wb = new Workbook("05-259-9999_V2_Stückliste.xls");
wb.Save("output-" + CellsHelper.GetVersion() + ".pdf");
Output Pdf Download Link:
output-126.96.36.199.pdf (72.9 KB)