Thanks for writing in!
Upon checking the website, I see it’s using old version of X Theme 6.5.6 and Cornerstone 3.5.5. Please update X Theme and Cornerstone to latest version which as of today is X 7.0.4 and Cornerstone 4.0.4 in order to avoid conflict and new version comes with host bug fixes and improvements. Once you have updated X Theme and Cornerstone, please clear cache and then reload the page and see how image renders in the preview panel.
Please take a look at following resources to update X Theme and Cornerstone: