GitHub GitBook PR preview disappeared

[DebbieAtSeam]

Sometime in the past day, the two GitBook PR preview "checks" stopped being added to the list of checks that get run for each GitHub PR. It looked like GitHub itself was reporting an outage of some kind, but they've now reported this outage as resolved. However, I'm not sure how to get the GitBook previews to reappear in the list of checks for each PR. Your help, please! Many thanks!