I am afraid, without your template file, we cannot evaluate your issue precisely to consequently figure it out. I think you may make your thread private and post your attachments, we will take care of your data and check your issue.
Well, you may skip PivotTables while loading your template file if this helps, see the following sample code for your reference:
var filePath = @"e:\test2\Book1.xlsx";
var loadFilter = new LoadFilter(LoadDataFilterOptions.All & ~LoadDataFilterOptions.PivotTable);
var asposeOptions = new Aspose.Cells.LoadOptions
//your code goes here
LoadFilter = loadFilter
var workbook = new Workbook(filePath, asposeOptions);
Hope, this helps a bit.