Hi Paul,
Thank you for using Syncfusion products.
The reported issue occurs in version 7.3.0.20 version. We have created the sample in version 9.1.0.20 and we unable to see the reported issue.
1.The Stacked Area Chart series are in the order acordingle.
2.The major grid line are is in horizondal axis line.
We have created screen video of sample execution taken at our side and placed the same in the below link.Please take a look at the video, try the sample at your side and let us know if this helps you.If you still face the issue, please revert back to us with the modified sample to proceed further on this issue.
We recommend you to upgrade to the latest versio 9.1.0.20.
Please let us know if you require any further clarifications.
Thanks,
Sridhar.S
F98487_video_17fa2566.zip