I’ve noticed this too. Private Relay is off. I’ve tried also disabling Safari content blockers, and still see some images fail to load, while others are fine. Generally the “hero” thumbnail on the feed view is visible, while tapping into the story in text or story mode has the broken image.
Here’s a story where some images load, and others do not:
Here’s xkcd feed with comic previews on feed, then tapping into comic with broken image:
I’ve found that opening in-app settings and deleting offline stories will make more images load for a short time, but then later the same images will show up as the “missing” question mark on blue square.
I’ve tried turning off completely offline stories, and that seems to help. So I think it’s a problem with the image caching on iOS specifically?