Plugin Settings Not Saving

Hello, I am looking to use this plugin one our posts page. On the settings page I’ve chosen to remove all but one of the featured image sizes, which is the size we would like our publishers of the site to use. All other thumbnail sizes I would like to be hidden from the cropping window, which is what I thought would happen when checking those sizes in the settings. However, all sizes are still displaying. Is this a known issue? Any help would be greatly appreciated. Thanks!