Hi there,
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.
Until we find a better resizer, you can do something like this: https://wpshowposts.com/support/topic/show-posts-images-not-working/#post-8324