Custom template second page returning 404

Hello,

Before anything, I have spent the past 3 hours browsing forums and trying to apply the solutions I found to my problem, but I just can’t get it to work.

I created a custom page template, I used the Page Navi plugin to get a custom pagination, but page 2 always returns a 404 error… frustrating.

Here is my page code :

<?php

 $paged = get_query_var( 'paged' ) ? get_query_var( 'paged' ) : 1;

 $args = array(
'category_name'=>"actualiteprincipale",
'posts_per_page' => 1,
'paged' => $paged
);

// Pagination fix
$temp_query = $wp_query;
$wp_query   = NULL;
$wp_query = new WP_Query();
$wp_query->query($args);

if ( $wp_query->have_posts() ) :
	while ( $wp_query->have_posts() ) :
	 $wp_query->the_post();  // Si pas vide

	 $url = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), array( 5600,1000 ), false, '' ); // On récupère l'image pour l'insérer après
?>

<div class="mainactublock" style="background-image: url('<?php echo $url[0]; ?>')">
 <div class="whiteborder">
  <h2 class="mainactutitle"> <?php the_title(); ?> </h2>
 </div>
</div>

  <div class="mainactudesc">
	<div class="row actupart">
	  <div class="col-md-12 col-xs-12">
	    <p class="mainactudate">Posté le <?php the_date(); ?>, il y a  <?php echo human_time_diff( get_the_time('U'), current_time('timestamp') ) . '.';?></p>
             </div>
	</div>
	<div class="row">

	<div class="col-md-7 col-xs-12 excerpt">
	  <?php the_excerpt(); ?>
	</div>

       <div class="col-md-5 col-xs-12">
	  <a class="mainactulink" href="<?php the_permalink() ?>" title="En savoir plus">En savoir plus</a>
	</div>
    </div>
</div>

<?php endwhile;
endif;
	wp_reset_postdata();
	// Custom query loop pagination
	wp_pagenavi();

        // Reset main query object
	$wp_query = NULL;
	$wp_query = $temp_query;
?>