Thanks for updating in!
1.) I was able to access the site. Please see the secure note.
2.) Yes a fatal error occurred which is why you cannot edit in Cornerstone.
There is an undefined call going on which resulted to a fatal error. Please make sure everything is up to date. Out dated theme and plugins will results to an issue.
3.) Please ignore the cache if you are not using CloudFlare or any caching plugins.
4.) You still need to update other plugins installed.
Please let us know how it goes.