@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