Hi there,
I am not sure why the system did not give the information, but you’d better use the forum itself to add the information and answers.
Anyway sorry for our late reply as we are getting a little bit of traffic due to the new releases of the theme, but it will be back to the normal mode in a week or two.
I accessed your website and added a new page using the Cornerstone and added the V2 Alert element with no problem:
https://www.moxie.design/test-page/
Then I tried to edit your contact us page and couldn’t do that. So I added a template of the same page called Test Template:

And added another test page and used the template to copy the same content. This time it worked. I added 2 extra dots here:

https://www.moxie.design/test-page-2/
This shows that the Cornerstone is working ok, and there are extra settings in the Contact us page which is not available on the Test Page 2 which is causing an issue.
I suggest that you try to add the settings in the Edit screen of the Test Page 2 and make it like the Contact us and on each step save and check if you can edit the page to find the problem.

I would also check for 3rd party plugin conflicts by deactivating all plugins except Cornerstone and test the case. If it is working ok then I would activate the plugins one by one and test to find the one responsible for the error.
Thank you