Hi there,
Sorry for not getting back to you sooner!
The image resizer only works if URL of the images matches the URL of the actual site. In this case, it sounds like ngrok is confusing the image resizer.
If you need it to work using ngrok, ditching the image resizing options and doing something like this might help: https://wpshowposts.com/support/topic/show-posts-images-not-working/#post-8324