Wordpress the_content / post is empty - wordpress

Question

I'm building my own template for Wordpress and I'm bumping into an issue when displaying the content of a post.
I have already built one page template for the home page and it works fine. The loop outputs what I want to display. Now I'm building the template to display an article but the loop doesn't return anything.
Here is the code of the page template:
<?php
/*
Template Name: PAGE
*/
define( 'WP_USE_THEMES', false );
get_header();
?>
<div class="wrapper">
<div class="sidebar">
<?PHP get_sidebar(); ?>
</div>
<div class="main">
<div class="section group">
<div class="col col12-12">
<span>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<?php endwhile; else : ?>
<p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
<?php endif; ?>
</span>
</div>
</div>
</div>
</div>
<?php get_footer(); ?>
This results in displaying the "sorry, no posts matched your criteria" message when i click on one of the links on the homepage. The strange thing is that the page really exists (it has ID=26 as you'll see here below):
<?php
$post = get_post(26);
$title = $post->post_title;
echo $title;
?>
This works and displays the expected title. I have tried get_the_ID(); to get the post ID but it returns an empty variable.
There is probably something missing in my template but I can't figure out what.
Any idea?
Thanks

Answer 1

I have found the issue and it had nothing to do with the template itself.
I discovered what's wrong by using one of the standard Wordpress themes (twentyfifteen) where every post led me to a 404 even if I clicked on a post from the Admin UI. I swapped back permalink structure to the ?p=123 option and there everything working. Definitely a permalink structure problem.
The problem was coming from the polylang plug-in. I'm using a network of wordpress site for which I have made this plug-in available. I did not need this plug-in for this particular site but somehow it needed to be active anyway. So I activated polylang and configured it to have only one language and now it works.
Got new gray hair in the process but if that can help anyone...
Thanks for your help!
Laurent

Answer 2

I don't think, that this template can output any posts like this. For WordPress
/*
Template Name: PAGE
*/
indicates: this is a page-template which you can asign to the content of a page but not to a post.
When you want to show a specific post on such a page you will have to:
Asign the template to the page in WP-backend
Add a new query to the template to show the post
Like:
<?php
/*
Template Name: PAGE
*/
define( 'WP_USE_THEMES', false );
get_header();
?>
// The new Query
$args = array (
'p' => '26',
);
// The Query
$query = new WP_Query( $args );
<div class="wrapper">
<div class="sidebar">
<?PHP get_sidebar(); ?>
</div>
<div class="main">
<div class="section group">
<div class="col col12-12">
<span>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<?php endwhile; else : ?>
<p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
<?php endif; ?>
</span>
</div>
</div>
</div>
</div>
<?php get_footer(); ?>
But as this is very complicated I would recommend to:
delete the /* Template Name: PAGE */ from the template
save it as single.php or more specific as single-26.php
link to the desired post in your wp-menu