Howdy,
Note: charts render correctly when executing application. Issue is with visual designer.
Current version: 2.51.7
In version 2.51.5 my charts rendered correctly in the designer. Now, after the update to 2.51.7, the designer shows an error where the charts reside.
Here's a basic Line chart definition:
and here's what the visual designer now shows for the chart preview after the update:

