We are unable to reproduce the issue at our end, it seems to work fine across iPad & iPhone. However, we suggest you to create chart instance once and update add datapoints in AJAX call instead of creating new chart instance for every datapoint. Also, instead of setting striplines properties using set method, we suggest you to update it through options and call render method once after updating all the options. Please take a look at this updated sample project for complete working code.
If the issue still persists, kindly share us more details like iOS version and the device in which you are facing issue so that we can try it out at our end to understand the scenario better and help you out.
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Manoj Mohan
Team CanvasJS