@aazimi,

Thank you for reporting the use case. It seems to be happening during different scenarios of the secondary Y-axis. We will revisit & reconsider this behavior in future releases.

As a workaround, you can add a dummy dataSeries attched to primary Y-axis as shown in the code-snippet below,

dataSeries.dataPoints = dataPoints;
data.push(dataSeries);   
data.push({type: "line"});

Please take a look at this JSFiddle for an example with complete code.

—
Adithya Menon
Team CanvasJS