There's no direct way of fixing this in my know. However, you can do one of the following to minimize the effect due to change in the layout:
1. Set the Styling Mode to Simplified and Sheet Object Style to anything from the dropdown but Glass.
2. If the design of your dashboards is affected by changing to Simplified, you can try setting the Styling Mode to Advanced and Sheet Object Style to Glass
Additionally, you may try removing the borders of this chart (or set the borders to 0 pt. See the following image to see how a chart without borders looks in webview mode. Since you are using multiple charts in the disguise of one, I think removing chart borders could be one of the easy solutions.
Please find the attachment.
Hope that helps