It happened on the home page. I clicked on the first photo and it came up with a ? instead of the photo. Scrolled through the photos and most of the others showed. Scrolled back and the first photo then showed. I wondered if it was something in Safari that was just taking a while to load the photos. My wife saw the same thing on her phone so it wasn't specific to my device. I don't remember seeing it in the past so wondered if it was something new like photo scaling or something like that.
