Looks like you're hitting this issue;
To resolve this, you should click that pencil icon in your Traffic Over Time visualization to get to the visualization editor. Then check the fields used in the visualization. The error seems to be caused by a field in the visualization that isn't in the docs, or that isn't aggregatable.
In my case, I found that earlier versions of Kibana allowed you to use fields which were not aggregatable in a visualization, but now that causes the error you are seeing.
If you don't see the problem, you can go to Management > Saved Objects > Visualizations tab export your Traffic Over Time visualization and upload the json file here and I'll take a look.
Regards,
Lee