Hi Leo,
Thanks for using Syncfusion products.
Sorry for the inconvenience caused. We are unable to reproduce the issue reported in your query. We have created a simple sample and test with chart "ZoomingAction" it is working fine in our end. we have created a sample based on your requirement with large points and Enable the "Zooming Actions". Zooming Scroll bar is used to just view the hide area of chart in both horizontal and vertical position.
Please download the sample from the link below here.
For more details regarding Zooming Action please refer our online document from the following link.
http://help.syncfusion.com/ug/windows%20forms/chart/Documents/491zoomingandscrolling.htm
Please let us know if you have any concerns.
Thanks,
Bharathiraja K.
ZoomAction_7e0b9c5e.zip