I want to mention, that our Dev Team needs more information for further investigation of the case.
Let us know what version of the Chart plugin you are using (with numbers).
Let us know the PHP version you are using.
Please provide us with an info, of what chart type you have chosen and what data is displayed in it.
Make sure, you are using the latest version of the plugin. If not, please update the plugin to the latest version and check the case that way.
If you are using a Cache plugin, then, please clear all the caches and exclude the link where the given chart is located from the Cache Plugin Settings. After clearing the caches, check the case with either the Incognito mode or another browser/device.
I want to mention, that we have already fixed the issue you are referring to in the 20.0.9.100 version. So, please log in to your account, download the latest version zip file and install it on your website.
You can make a DB backup before installing the zip file for your safety (you can use Updraft Plus).
As you are using the Pro version of the plugin, please contact us via this form for premium support and further discussion. Our customer care specialists will always be happy to help you.