If more series are in the same axis, the series of type area must be the first of the axis, otherwise, the chart shows a line chart.
Steps to Reproduce
- Define a new chart.
- Add a series (A) and set the chart type to line
- Add the second series (B) and set the chart type to area
As you should see, the B is a line chart and not an area chart.
If you move the B series before the A series, B became an area chart.