Extra column when editing Line chart with simple editor

[Mara42]

Description

When editing/creating a Line chart and editing its data with Simple editor, if you change the name of the last columns (all of them or just one but not the first one; if you change the name of the first column the plugin will work as it should), and then click Show Chart, an extra column will appear (the one that actually was renamed in the previous step if we renamed one, or the last one we renamed if multiple columns were modified). And if we go back and try to edit it with the simple editor there is no way to see this additional column (even though it is displayed in the chart legend).

Step-by-step reproduction instructions

1. Make sure to have Visualizer installed and start to edit/add a page
2. Click on plus and Select Visualizer Chart
3. Select Create New Chart and select Line Chart
4. Select Simple Editor and click on Edit Data
5. Rename the last columns (you can rename any column except the first one to see this behaviour)
6. Click on Show Chart

Screenshots, screen recording, code snippet or Help Scout ticket

Rename one of the last columns:

Extra column showing

Click on edit and the column is not there

Environment info

https://pastebin.com/wS1tsBvP

Is the issue you are reporting a regression

No