amp_post_template_file doesn’t work

I’m developing in localhost an AMP version for a live website.
Only one thing is not working well. The custom template for the homepage is not called.
I did these steps:

[x] Add add_theme_support( 'amp', array( 'template_dir' => 'amp-templates', ) ); to my functions.php;
[x] Check all boxes in AMP Settings;
[x] Go to Pages, EDIT my Homepage and ENABLE AMP;
[x] Add the code below in my functions.php

function xyz_filter_home_and_blog_amp_post_template( $template, $template_type, $post ) {
	if ( 'page' === $template_type && 'page' === get_option( 'show_on_front' ) ) {
		if ( (int) get_option( 'page_on_front' ) === $post->ID ) {
			$template = dirname( __FILE__ ) . '/amp-templates/front-page.php';
		} elseif ( (int) get_option( 'page_for_posts' ) === $post->ID ) {
			$template = dirname( __FILE__ ) . '/amp-templates/blog.php';
		}
	}
	return $template;
}
add_filter( 'amp_post_template_file', 'xyz_filter_home_and_blog_amp_post_template', 10, 3 );

But when I access http://localhost/mysite/?amp (my homepage), the main file front-page.php inside the template root is still called.

Curiously, the AMP is working on this page, because the files header.php and footer.php inside the root template directory is calling AMP code.

All the other templates/custom templates are working fine.
In addition to creating the file theme-root/amp-templates/front-page.php I created the file theme-root/amp-templates/index.php and still not working.

I tested with these 2 files and WITHOT the filter amp_post_template_file and still no working.

Another curious thing is: I put this ECHO in the function:

function xyz_filter_home_and_blog_amp_post_template( $template, $template_type, $post ) {
	echo "CALLED!";exit;
	if ( 'page' === $template_type && 'page' === get_option( 'show_on_front' ) ) {
.....
}
add_filter( 'amp_post_template_file', 'xyz_filter_home_and_blog_amp_post_template', 10, 3 );

If this filter was triggered, the page have to break and prints only the word: CALLED
But, after insert this echo and reload the homepage, the page loads regular. In other words, the filter is not triggered.

Someone knows what I’m doing wrong?
Tks!