I have observed the issue and request you to please try Aspose.Slides 18.5 on your end as well and share results. Please also provide source presentation and sample project for reference as well.
Aspose.Slides for ,NET 18.5 does not support .NET Core. However, it is still usable with Mono platforms. As requested earlier, please provide the sample project and environment details on your end so that we may perform testing on our end.
Thank you for sharing the requested information. An issue with ID SLIDESNET-40277 has been created in our issue tracking system to further investigate and resolve the issue. This thread has been linked with the issue so that you may be notified once the issue will be fixed.