One of the beauties of WordPress is also one of the main challenges: 3rd party plugins. This is further exacerbated when you attempt to make two uniquely developed tools interact seamlessly. It's one thing if one company controls the code end to end, but regretfully that is not the case with 3rd party plugins.
We've discovered that due to the way certain 3rd party plugins load their scripts and styles there is no way to consistently show a live preview of these Elements in the Content Builder. For these plugins (Revolution Slider, Essential Grid, and The Grid), we've added a new message pictured below. We have not found any issues with LayerSlider or Contact Form 7, so if you use those as an Element you should continue to see the preview. The front end of your site will continue to work as it always has.
NOTE: This is different from adding Revolution Slider in the header. Those will continue to show in the preview. We are only talking about when the above 3rd party plugins are used as Elements on a page or post.
If the preview is not available due to how that plugin is loading their scripts or styles, you can click "View Live” at the end of the message to open the content in a new tab so as to see the Element on the live page. Don't forget to save the page first. This change will take place in X 6, Pro 2, and Cornerstone 3.
Going forward, we will review any 3rd party plugin Elements on a case by base basis. If the plugins are developed in such a way as we can consistently preview the plugin output, we will do so otherwise the text below will be used.