Can you edit that label or section topic and add the image 2 times in a row to see if both break when viewing on the course page, or if only the first one breaks?
Also, when you are using developer tools -- does the image URL change for that broken image (versus when in Editing mode)?
I had a similar issue that happened once in a while (but it happened across Chrome, Safari, and FireFox
). I never figured out why the image looked fine when i had it open in Atto, but broken on the activity page/course page, but I did notice it didnt matter what the image was, it was just the 'first' image was breaking. If i copied the img tag and had 2 in a row, then both looked good in Atto , but as soon as i saved, then the first image was broken and when I inspected it with browser tools, the URL was being slightly changed (I can't recall to what off hand, I think it was removing "src" and adding something else). Remains a mystery to me but maybe related to your issue so figured I'd share...