Thanks for using Syncfusion product.
You can avoid the change of interval after zooming by using VisibleRangeChanged event. In this event you can set the desired value to the interval of VisibleRange property, so that when the chart is zoomed also the interval will be same. Kindly find the code snippet below.
this.chart.PrimaryYAxis.VisibleRangeChanged += PrimaryYAxis_VisibleRangeChanged;
void PrimaryYAxis_VisibleRangeChanged(object sender, EventArgs e)
((Syncfusion.Windows.Forms.Chart.ChartAxis)sender).VisibleRange.Interval = 5;
Screenshot before zooming:
Screenshot after zooming:
For your reference we have attached the sample. Kindly find the sample from below location.