Why isn’t template_include working with AMP correctly?

Your endpoint is only applied to posts, add EP_PAGES to generate rules for page post type-

add_rewrite_endpoint( 'amp', EP_PERMALINK | EP_PAGES );

That should also be within a function hooked to init.

Related Posts:

  1. Get template name by full URL
  2. Template Include crashing browser
  3. problem including page template
  4. Include Template Based on User IP Address
  5. unexpected T_FUNCTION in plugin template [closed]
  6. Use TEMPLATEPATH for custom url
  7. php include returns 1 after content
  8. Is there any way to use get_template_part() with folders?
  9. Methods of Integrating Plugin Data with Themes
  10. Use template_include with custom post types
  11. template_include for search.php makes WordPress think its on the home page
  12. Render a different post/template from within the template_include action?
  13. Custom Endpoint Gives 404 Header
  14. WordPress rewrite rules for state and city
  15. template_include not loading -instead goes to index.php
  16. Link to file in plugin directory from wordpress template?
  17. Is it safe to include a javascript file in a template’s php file?
  18. How to check if txt file exists inside template folder?
  19. For custom templates, is it better to use `template_include` or `type_template`?
  20. Put CSS inside a PHP file and include it the right way
  21. locate_template function – File not getting included
  22. How do I go about looping through a advanced custom field on a particular page inside of another page
  23. Content vs Template on custom post
  24. A include_template Question
  25. template_include filter does not render the custom template
  26. How to use template_include hook with form submission?
  27. WP overwrites my setup_postdata() setup
  28. Replace wp_query with wp_user_query
  29. Pull in an “Include” file based on a WordPress Category ID
  30. template_include doesn’t work with child theme
  31. How to include a page template and template part into my plugin
  32. Should I use do_action in the header file?
  33. Redirect page to homepage, keeping URL
  34. How to add variables to a template
  35. Why is WP template_include overwritting all templates rather than specified page?
  36. require happens out of order
  37. Using require_once for parent-directory not working but is working in sub-directories
  38. Theme parts path location dump
  39. wp_mail: Using file_get_contents to include template in message
  40. Why does get_post() return the latest post inside template_include before doing anything
  41. Should I use include(_once) or require(_once) for loading php-file with customizer settings?
  42. How do I update the SEO information on dynamic pages being generated from template_include?