The preview could not load due to the iframe response being incomplete. This is most often related to a plugin conflict, or customizations introducing a PHP error.
I have a clean installation of X and this keeps showing.
I’ve no plugins installed and don’t use SSL
I’ve read https://theme.co/apex/forum/t/cornerstone-fails-to-open-editor-on-any-post-page/29118/2 and didn’t understand what to do. Please help me.