URLs are exactly the same for both.
On the image that have a thumbnail, when I click, I see a full preview of the image with the “edit” button below. On images that did not successfully upload there is no preview, but there is the “edit” button. And once I click on the edit button I can see a smaller version of my photo with very basic options for rotating and such.
If I follow the URL of the images that I don’t see the thumbnail. I CAN see the image in my browser.