Thanks for providing us some details.
Well, the issue might be on your end or in your code. Please check individual variables and objects data if these have correct values, e.g reportSheetName, exportData.DataTable.Tables.Rows.Count, etc. You may even try some hard coded values to directly assign for CategoryData attribute.
If you still think it is an issue with Aspose.Cells APIs, kindly do create a simple console application (runnable) and post us (you may zip the project prior attaching) to reproduce the issue on our end, we will check it soon. Please remove any inter dependencies for external database or external sources and use/create DataTable in code (if necessary), so we could evaluate your issue precisely to consequently figure it out soon.