Thanks for asking.
I see that you have Cornerstone 1.2.4 installed on the website. I can't proceed to update plugins on your website as we are not supposed to fiddle with core working of customer website on a live environment.
It's mentioned in the ticket that you have tried to update manually. But I request you to please try out following solution. First, please delete Cornerstone completely from Plugins > Installed Plugins > Deactivate Cornerstone and then delete. Try logging to FTP and under /wp-content/plugins/ delete Cornerstone directory. After that please visit X > Validation and should install latest version of Cornerstone automatically.
If you face issues, please share FTP details in a secure note with us as well and kindly give us the permission to make necessary changes on the website.
Kindly let us know how it goes.