From the News from PlayCanvas post ‘Engine Release 1.50.0 - Clustered Area lights ’
This is because in the hierarchy, Entity ‘Sample’ does not have an element component.
All UI entities under a screen need to have an element component throughout the hierarchy otherwise some functionality doesn’t work.
Making the ‘Sample’ Entity an Image Group that is always fullscreen fixes the issue as seen here
I have a ticket here to add a warning in these scenerios.