Hello,
Like others previously posted on the forum, I’m experiencing this error very often.
The only way to resolve it is to refresh enough times for Cornerstone to decide to finally show the preview properly.
I’ve looked at all the other suggestions or workarounds to resolve this, and I haven’t been able to get it to stop appearing.
We have been able to increase the PHP memory to 512MB and get it updated to version 7.0. We deactivated all third party plugins, including WP Rocket, however it is still happening with just Wordpress and X Theme together.
Any help with finding the reason behind this issue would be really helpful.