get_template_part() Not Working in Loop

Thinking about my comment…wouldn’t it be simplier to say:

<section id="content" class="site-content blog-page">

<div class="container">              
<?php if ( is_home() || ( is_front_page() && is_home() ) ) : ?>  
    <?php if (have_posts()) : while (have_posts()) : the_post(); ?>
            <h2> There are posts but template parts aren't found </h2>         
            <?php get_template_part( 'template-parts/post/content', get_post_format() ); ?>                 
            <?php get_template_part( 'template-parts/navigation/navigation', 'pagination' ); ?>  


    <?php endwhile; ?>

    <?php else : ?>
        <h2> There are no posts.</h2> 
    <?php endif; ?> 
<?php else : ?>
    <h2> THIS IS not home or front </h2>   
<?php endif; ?> 
</div><!-- Ends .container -->       

try this, so now we know if it’s not home or if it’s no posts or if it can’t find your templates..