We've had a user report this issue and I've just recreated it on a mac on chrome. When you upload a new post and add a photo, onec you click publish, the post appears as a big white box with a tiny generic thumbnail in the top left and the word 'post image'. When you click on 'post image', a pop-up appears that tries to load the image for an infinite length of time. Screenshot attached.
Think this is (was) a cdn issue. Seems to work for me now. If you right click and either copy image address (and paste) or open image in new tab can you see the image?