We’ve bumped the internal version of Kookaburra Page from 1.3.1 to 1.3.2, while keeping Backlight at 5.3.1. This is a hotfix for a bug introduced to Kookaburra’s new essay features in the 5.3.1 update.
If already running Backlight 5.3.1, please visit the Backlight Modules page of your admin to install the latest version of the Kookaburra Page module.