Harlowe's content render process has an issue with displaying block based HTML elements like <div>, it causes the displaying of the content of such elements to be at different transition rate that the other content of a Passage.
This answer to the Using headings (markdown or html tags) causes a delay in displaying text question explains how to use CSS and the display: inline-block property setting to overcome this issue.
In this specific case you would target the div element in the CSS selector, which the last example in that answer demostrates.