Hi Xavier,
Greetings from Syncfusion.
We have analyzed the reported scenario with the attached screenshots. Yes, it is a bug and it has been fixed in version 16.4.0.40 for chart rendering in SVG mode. So, either you can upgrade to your version to resolve this issue or kindly revert us with your version details, we will provide you the patch in appropriate version.
If you are rendering the chart in Canvas mode, then the fix for this will be included in our upcoming volume 1 main release which is expected to be rolled out at the end of March 2019. Kindly revert us with the above details to provide you the solution sooner.
Thanks,
Dharani.