Hi Gary,
We should get the same issue if it’s related to the theme or cornerstone. Plus, the issue is with the functionality within Envira features which aren’t related to the theme.
I created a sample grid and it works, looks like your existing grid’s data is corrupted. Please try re-creating them, we don’t have control of how Envira processed their data so we couldn’t really dive deeply into its core troubleshooting.
http://architecturesurrey.co.uk/wp_arch/x-test/
Thanks!