OK,
So I have seen a few of these problems, mostly dated to last year. When you Edit with Cornerstone, the builder loads, then reloads to another screen “Howdy!..”
So I have taken all the steps to isolate this issue such as:
Fully updated
clear cache
increase memory limit
deactivate plugins
etc.
Once all that was done, I tested: Worked Fine.
So I started to reactive plugins and test 1 x 1. Immediately I found the problem to be Woocommerce. Can you please check what the problem is. I can’t edit in Cornerstone.