Our resizer only works with locally hosted images as of right now. For example, they need to be served from the same domain/server as the page you’re looking at.
Since you’re using a CDN, that domain/server is different, which is why they won’t work.
Thanks for following up. That’s good to know, but the problem did get resolved when I removed the image dimensions from the plugin settings, so it doesn’t seem like the use of a CDN was an issue, at least not for me in this instance.