I have the PRO theme and got the message: "The preview could not load. This is most often related to a plugin conflict or aggressive page caching. Checking the developer console for errors could indicate what went wrong."
I tried to deactivate all non-Themeco plugins and it was still the same. I looked in the developer console and it says: "Failed to load resource: the server responded with the status of 500 () and preview-frame update-aborted::
Then I cleared the style cache but still nothing. Then I changed the wp-config.php file to increase the PHP memory to 512 MB and still nothing ...
What else can I try?