Thanks for your posting and using Aspose.Cells for Java.
We were able to observe this issue. It worked fine with older version but with latest version, it is not working good.
We have logged this issue in our database for investigation. We will look into it and fix this issue. Once the issue is resolved or we have some other update for you, we will let you know asap.
This issue has been logged as
CELLSJAVA-42086 - Background image in chart is wrong