Well, please make sure that your licensing code should run at least one time in the whole life cycle of your Java application, it looks like your licensing code does not process at all. Please make sure that licensing code should be run at least one time in your whole application life cycle, you should place the licensing code at a place where it should be processed first and fine before using any other APIs of Aspose.Cells component. For example, you may place the licensing code in your class library which it should be run when you create object for that class library (e.g in the constructor) before using any other APIs of the product. You may debug your scenario/ case and figure it out by yourself.
Also, please see the document for your reference: