The file was deleted or has expired in the file manager (a filename with an expiry date is purged after it). Then: the path has a space or special character that was not URL-encoded; the URL carries resize parameters or a .webp extension on a filename of type file, which cannot be transformed; the file sits under templates/, which is never served; or its extension is not in the static-asset allow-list. An <img> printed from a hand-built path rather than the image object has no fallback when any of these is true.