I have created a new release: https://github.com/mendix/ChartJS/releases/tag/v3.1.0. This will fix the issues regarding the legend and the animations. This will be updated in the AppStore soon
This widget hasn't been updated for a long time, so I just began implementing new features and fixing issues. Any issues regarding this widget, please add them to Github. As for the legend, you are right. I have been looking into it as well.