Why do blank lines disappear from Instagram captions?
Two things happen. First, when a line ends with a space, some Instagram clients treat the following newline as part of a wrapped line rather than a paragraph break, and the blank line collapses. Second, some app versions strip lines that contain nothing at all. Removing trailing spaces solves the first case without adding anything to your text. The only workaround for the second is an invisible character in the blank line, so that option is off by default and marked in the preview when it is on.