Yes I was fully updated and updated again this morning to cornerstone 3.1.5 and the theme to latest too. But cornerstone/xtheme editing view is still broken when I add the envira gallery to the page, refresh the page or leave and come back to the page.
Ok I think I have identified the problem.
I had a slider revolution banner inserted using a short code in an element at the top of the page and Envira gallery via a short code at the bottom of the page. When the two were on the page together it would break the view in cornerstone completely. Remove either one and the cornerstone layout view would be OK again.
So to fix it, I instead added the slider revolution via general page settings / Slider Settings: Below Masthead and hey presto I am able to have both elements on the page without breaking cornerstone view.
So I presume the deeper problem is a conflict between the way the two elements display on the page via short codes.