Only one Pingback working

Hi,
I recently made a post that had two links to previous posts in my blog. A pingback showed up for the first link (in the first paragraph of the new post) but not to the second link (in the last paragraph).

In this case it seemed fitting as the second link was less related to the post, however I’ve been looking back and seeing I’ve been having spotty luck with automatically pinging back to posts.

I looked around… is there a rule to only pingback in the first paragraph? Or is there something I’m missing?

Thanks!