Steps to reproduce

1. Define your custom styles in a simplified way.

ezpublish:
    system:
        admin_group:
            fieldtypes:
                ezrichtext:
                    custom_styles: [highlighted_block, highlighted_word]

ezrichtext:
    custom_styles:
        highlighted_word:
            inline: true
        highlighted_block:
            inline: false

2. Add Folder or Article with Custom style (either block or inline)
3. Observe

• default custom style templates not rendered in Admin view mode and front-end site.
• warning in var/logs/<your-env>.log: "app.WARNING: Template style 'highlighted_block' default configuration was not found"