Hi
I have solved this issue myself, thanks for looking.
The issue seemed to lie in the custom name of the theme and use of that in the style.css
I exported the settings before the below.
I uploaded a new version of the theme, enabled that, imported the settings, hit save.
Website working, and Advanced builder now working!
Hi
Enabled the theme editor as requested.
Disabled security plugin > Layout editor still would not appear.
Have disabled all plugins, and still issue is present.
Sure login in private box