Thank you for writing in, please update your Cornerstone to v3.5.4. Remember to clear all your caching features (plugin, server-side, CDN, and browser's cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Another thing, I see that the images on slider (on wpengine staging) are still requested from live URL (
https://rustandrefind.com/), please edit your slider and re set those images.
Hope it helps,