Infinite Scroll: Twitter embeds not displayed correctly on pages past first load

#### Steps to reproduce the issue

1. Activate a theme that displays the full post on the blog page, like Twenty Fifteen or Penscratch.
2. If the theme has any footer widget areaes, make sure they are empty and do not contain widgets.
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. Create 10 posts, adding a Twitter embed to each post by pasting a single line like `https://twitter.com/wordpressdotcom/status/884332652765032448`
5. Visit the front end and scroll down the blog.

#### What I expected

As I scroll down the blog, Twitter embeds should be displayed fully in the "card" format, with any images displayed. Example:


#### What happened instead

As I scroll down the blog, Twitter embeds **below the first page load** (example URL structure: `https://yourgroovysite.wordpress.com/page/2/` do not display the correct "card" format, but instead show a simple blockquote format.

Example:


Replicated with Independent Publisher 2, Quadra, Penscratch 2, Twenty Fifteen.

## Screencast with Twenty Fifteen

https://cloudup.com/co14xQm3DgR

Reported in: http://en.forums.wordpress.com/topic/quadra-circa-hexa-question-pages-pages

Reproduce the issue on the front end with Infinite Scroll enabled, comparing Twitter embeds in the initial posts with those loaded from the page/2/ URL structure. Verify the behavior across the listed themes; done means every loaded embed uses the full card format and displays its images.

Written by the indexing model from the issue text.