Im dynamically generating dataPoints and sometimes, objects with null value will not be added to datapoints. This confuses the stackcolumns chart. displays some column names twice.
I got around it by forcing zero y values to the objects.
It’s not a bug. Conceptually, a Stacked Chart is supposed to Stack Data Points from multiple Series and if any/all series don’t have Data Points at a certain point, it is not possible to stack them. i.e. When null values are used, it is not possible to stack them and the results are unpredictable. So its recommended to use zero instead of null.