Hi Andreas,
Thank you for your interest in Syncfusion products.
I am able to see the issue that you have mentioned. But this issue can be solved by setting the numberformat. Please refer the below code snippet:
[C#]
sheet1.Range["B5:B14"].NumberFormat = "dd/mm/yyyy";
//Create Template Marker Processor
//Northwind customers table
ITemplateMarkersProcessor marker = workbook.CreateTemplateMarkersProcessor();
marker.AddVariable("Customers",northwindDt);
marker.AddVariable("NumbersTable", numbersDt);
//Process the markers in the template.
marker.ApplyMarkers();
Here is the sample for your reference:
http://websamples.syncfusion.com/samples/XlsIO.Windows/F-73327/main.htmPlease have a look at the above sample and if still the issue exists, could you please try reproducing it in the above sample and send us the modified sample so that we could sort out the cause of the issue and provide you a solution?
Regards,
G.Yavana