@ehudg,
The behavior is designed such that zooming is limited upto a certain region, so the user doesn’t end up zooming into a blank-region (region with no dataPoints). To zoom into a certain region, there should be a minimum of 3-4 dataPoints.
In your case, the zoom doesn’t work as there are less than 3-4 dataPoints over the Axis Y.
We will reconsider this behavior for future releases.
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Indranil Deo,
Team CanvasJS