Graph - Problem with Stacking

goal of the graph:

show numebr of defect per month stacked based on the status


not existing values are shown :frowning:

So there should not be any defect in sate verification in 2020-03 und 2020-04

Has anybod an idea what should be changed or is this a bug in the graph panel?

Here are the settings of the graph panel

any idea about this issue?