Thanks for your posting and using Aspose.Cells.
Please download and try the latest version: Aspose.Cells
for .NET v188.8.131.52 it should fix your issue.
I have tested your code with the latest version and it generated correct output excel file. I have attached the output excel file for your reference.
Can you please check again this issue? seems it’s present again in version 184.108.40.206.