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.
If your issue still occurs then please provide us your runnable sample console application project replicating this issue with the latest version along with your source excel files used in your code.
We will investigate this issue by running your project and then update you how to fix the issue. In case of some bug, we will log it in our database for a fix.
Thanks for your cooperation.