Thank you for your reply. I checked your example in the provided link, and my problem happened again with the following circumstances.
1- open the console section in the below of chart and drag it up as much as the chart will not need the scrollbar. (the chart should have the minimum height without scrollbar)
2- now, zoom the chart and hover the mouse on toolbar to show the tooltip, then scrollbar will be appear.
3- click on reset, now the scrollbar disappear.