Templates aren't called in custom module?
Your problem is coming from this code:

$theme_registry['page']['path'] = drupal_get_path('module', 'example_ch_hero_panel') . '/templates';


The first array key, page, means you are working the page template. You've told the system to look for page.html.twig in your module's /templates directory. It's not finding it, so you get that error.

Remove that hook altogether, it's not the right way to do what you are trying to do.