I recently moved all my websites to Azure (don’t judge.. they gave me a really good deal lol). Anyway when I tried to add pictures to a new WordPress post, they wouldn’t appear. The small preview images, or thumbnails, were working fine (in the media library) but no such luck on the websites.
Apparently when uploading files the server first saves them in a temporary folder before moving them to the right folder within the website’s content.
The issue was that the server user had limited access to the temporary folder, so all files going through it had the same limited access. I gave the server user more access to modify the files (though I’m not sure if read-only access would have been enough), and now all uploaded files have better access for the server user, making them visible on the website.