Greetings from Syncfusion.
We have analyzed your query. we have prepared a sample based on your scenario. Unfortunately, we are unable to reproduce the reported issue. When we click to print the chart, there is no unexpected line in charts. Sample used for testing, can be found from below link,
Kindly modify the above sample or replicate your sample to replicate your reported scenario which will be helpful in furthermore analysis and provide you the solution sooner.