Hello Mike,
I just tested with the X-theme and Cornerstone and the Image Zoom button shows up in the editor as normal.
In the FAQ page you’ll find a known incompatibility with the Black Studio Tiny MCE Widget plugin and SiteOrigin Widgets Bundle. If this is not your case, maybe you can give me a list of active plugins on your website so I can test further.
There is also a solution for applying the zoom without the Image Zoom button in the editor: when you add a CSS class called ‘zoooom’ to any image, the zoom will be applied on that particular image. Remember that the zooming works only when the displayed image is smaller than the loaded image (i.e. the image is shrinked with “width” and “height” attributes).
