Very odd.
My only guess is that there are a couple of hidden columns to the right of your data that were selected when the chart was created. Empty columns with no label in the header row would produce results like those shown in your chart.
You could hide the two blocks with a rectangular Shape, filled white, with no border and no shadow, and resized to just cover the two extra markers, Use Arrange > Bring to Front if it slides in behind the blocks. Grouping them with the chart would also be useful, but considering that they and the chart are quite different objects, Grouping may not be possible.
Regards,
Barry