Custom-ui extra_data_template and extra_badge not working

I’m missing something–hopefully obvious in my configuration of Custom-UI.

All my uses of templates for icon_color, icon, state. etc. with custom-ui work great. But I can’t get any extra_data_template or extra_badge to work.

Here is my customize:

light.arc_lamp:
  icon: mdi:lamp
  extra_badge:
    - attribute: brightness
      unit: Br
  extra_data_template: 'test'

In frontend: I have the appropriate files linked directly to github. I even tried installing the customizer plugin which I believe makes it unnecessary to have the frontend: links. I also have the setting in customize_glob: which also appears to be unnecessary.

I’m have them in a basic entities card:

entities:
  - entity: light.arc_lamp
type: entities

All I get is:
image

What could I be missing?