Thanks for your posting and using Aspose.Cells for .NET.
We were able to observe this issue. When we check the Series property, Automatic fill is selected although Gradient fill has been applied. We have logged this issue in our database for investigation. We will look into it and resolve this issue. Once, the issue is resolved or we have some other update for you, we will let you know asap.
We have looked into this issue. It seems to be MS-Excel bug. We used MS-Excel
to create an Excel file with gradient fill bubble chart and saved it. Then we re-opened the
file and found the fill of series is automatic. This only occurs to bubble
charts.