[Plugin: Jetpack by WordPress.com] Infinite Scrolling no post-load event

I’m using the latest _s theme with the Jetpack by WordPress.com plugin for infinite scrolling.

Posts are loading as expected, but the post-load event never fires.

I’ve read through the tutorial at http://wptheming.com/2013/04/jetpack-infinite-scroll-masonry/, as well as searched and found similar unresolved issues (https://ww.wp.xz.cn/support/topic/infinite-scrolling-post-load-event-does-not-fire).