Hi there,
Please kindly consider that the latest version of The Grid plugin which we support is 2.4.0. We did not test the Cornerstone with the version you have mentioned. You will need to wait till we release the update which seems to be something in line with our theme and Cornerstone release as you reported it is not working at the moment.
You will need to roll back to version 2.4.0. at the moment. We will inform our development team that there might be a problem with the new version of the Grid and the Cornerstone preview.
Thank you for your understanding.