Earlier today, WordPress 5.3 got release. Unfortunately, this seems to have affected Jetpacks related posts. Instead of centred, the related posts were suddenly left aligned. I went ahead and added the following code to my site, which not only centred the related posts but also made that container wider. This is the CSS code I’ve added to my site:

// Centre and widen Jetpack's related posts.
#jp-relatedposts {
  margin-left  : -100px;
  margin-right : -100px;
  max-width    : 1024px;
  margin: auto;
}