We tested the scenario in our environment using one of our sample files and Aspose.Page for .NET 20.11. We were unable to notice the issue that you mentioned. Would you kindly share your sample XPS file with us so that we can test the scenario in our environment and address it accordingly.
Aspose.Page for .NET supports .NET Core. However, we were able to notice the issue at our side and have logged it as PAGENET-222 in our issue tracking system. We will now work over resolving it and let you know as soon as it is fixed. Please give us some time.