Infinite Scroll: Simple Payments buttons do not render on blog page

#### Steps to reproduce the issue

1. Activate a theme that displays full post on the blog or archives page. I tested this with Sela Theme (front page set to latest posts) and found the issue originally with a user case on Orvis Theme
2. Remove any footer widgets to ensure infinite scroll is made to work.
3. Activate infinite scroll (WordPress.com - WP Admin > Settings > Reading > "Check to load posts as you scroll." or self-hosted, Theme Enhancements: "Load more posts as the reader scrolls down")
4. Set `Blog pages show at most` to about 4.
5. Create 10 posts with a Simple Payments button embedded in each of them.
6. Visit the front end of the blog and scroll to load new posts.

#### What I expected

I was expecting to see the simple payment button within the posts loaded by infinite scroll buttons.

#### What happened instead

I was able to see Simple Payment buttons for the first 4 posts that loaded without infinite scroll.

However, the next few posts that loaded with the infinite scroll feature, the payment button was not visible. This is also true if you use the `older posts` button when infinite scroll is deactivated.

**Screenshots**

#### Additional observation

I noticed that the `

Reproduce the issue with a full-post theme, Infinite Scroll, and Simple Payments buttons, then compare the initial posts with posts loaded by Infinite Scroll or the older-posts button. Review the related issue #7445 for context. Done means Simple Payments buttons render in all loaded posts, with the reported empty container no longer occurring.

Written by the indexing model from the issue text.