This is a reproduction of the infinite-loop issue described in gatsbyjs/gatsby#11364.
Steps to reproduce:
yarn install
gatsby develop
Note that there is a Maximum call stack size exceeded
error in the console. This is due to the circular references in Contentful: Article A has a reference to Article B in its rich-text body, and vice versa. You can try viewing the actual content in Contentful's Discovery app, but it currently has some JS errors that are preventing it from working.