The latest version of WPML Multilingual CMS (3.3.7) prevents updates to pages made with Cornerstone from saving properly. I tested with all plugins except Cornerstone deactivated and was able to trace it to WPML.
Another support here, would you mind providing a screen recording of what you’re currently getting? I checked it and saving works okay, though I’m not sure if I’m doing the same thing as you do 🙂
Sure, you can revoke your existing key at your license page here in the forum. Then simply generate new for your staging site, then last, validate it to your staging site.