No, there is no limitation regarding total number of images (probably you are using Sheet to Image feature) generated in licensing mode (licensing mode is that when you set a valid license before using any other APIs of the product), you should be able create as many images as you want for sure. The license is set forever in an application life cycle, it should always work fine.
It looks like licensing code is not called all the time as you use static variable for license for your scenario. Please make sure that your licensing code should run at least one time in the whole application/service life cycle, it looks like your licensing code does not process all the time. You should place the licensing code at a place in your program/class where it should be processed at first and fine before using any other APIs of Aspose.Cells component. For example, you may place the licensing code in your main class library which it should be run when you create any object for that class library (e.g in the constructor of the class) at the start before using any other APIs of the product. Moreover, we also recommend you to kindly check if the license is actually set/ loaded fine, see the document for your reference:
We are creating some images based on an excel at the very start of the application, and it also works for up to a week. But then without any service restart, the license becomes invalid somehow.
I’ll add the check IsLicensed, and then set the license anew.
I’ll also try to add some logging to it in order to see when this happens.
Well, we added this feature a few months back. We recommend you to kindly try the recent versions (e.g Aspose.Cells for .NET v8.6.2 is the latest version) of the product.