Double pagination on post

Hi Tom / all--

You've helped a bit on this is in the past, so hopefully you have an idea here. I'm not sure when it broke, unfortunately, and I can't seem to figure out the fix. My blog is a webcomic, where it's important to have pagination above and below the post. I have this, but I somehow now have double pagination below the post.

If you go to the main page of the site, you'll see the pagination is correct. But if you click any of the pagination links (which takes you to a post) you'll see the double pagination below the post.

This is what's in my child theme functions.php:

<?php

add_action( 'generate_before_main_content', function() {
    if ( function_exists( 'previous_post_link' ) && function_exists( 'next_post_link' ) ) {
		echo '<div class="post-navigation">';
		echo  previous_post_link(); //Older Link using max_num_pages
		echo  next_post_link(); //Newer Link using max_num_pages
		echo '</div>'; 
    }
} );

add_action( 'generate_after_main_content', function() {
    if ( function_exists( 'previous_post_link' ) && function_exists( 'next_post_link' ) ) {
		echo '<div class="post-navigation">';
		echo  previous_post_link(); //Older Link using max_num_pages
		echo  next_post_link(); //Newer Link using max_num_pages
		echo '</div>'; 
    }
} );

add_filter( 'next_post_link', function( $output, $format, $link, $post ) {
	
	$currentID = get_the_ID();
  	$args = array(
	  	'numberposts' => 1,
	  	'order'    => 'ASC',
	  	'orderby' => 'rand',
	  	'post__not_in' => array( $currentID ),
	);
  
    $random_post = get_posts( $args );
	
    if ( ! $post ) {
       	  $next = sprintf(
        '<a class="next-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $post ),
        $post->post_title
	);

	  $random_post = sprintf(
        '<a class="random-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $random_post[0]->ID ),
        get_the_title( $random_post[0]->ID )
    );
	
	$last_post = get_posts( 'numberposts=1' );

    $last_post = sprintf(
        '<a class="last-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $last_post[0]->ID ),
        get_the_title( $last_post[0]->ID )
    );
	      return $random_post . $next . $last_post;
    }
	
	else {
		  $next = sprintf(
        '<a class="next-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $post ),
        $post->post_title
    );
  
    $random_post = sprintf(
        '<a class="random-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $random_post[0]->ID ),
        get_the_title( $random_post[0]->ID )
    );
    
	$last_post = get_posts( 'numberposts=1' );

    $last_post = sprintf(
        '<a class="last-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $last_post[0]->ID ),
        get_the_title( $last_post[0]->ID )
    );
	   return $random_post . $next . $last_post;
	}
	
}, 10, 4 );

add_filter( 'previous_post_link', function( $output, $format, $link, $post ) {
    if ( ! $post ) {
        $prev = sprintf(
        '<a class="previous-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $post ),
        $post->post_title
    );

 $latest_post = get_posts( 'numberposts=1&order=ASC' );

    $latest_post = sprintf(
        '<a class="latest-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $latest_post[0]->ID ),
        get_the_title( $latest_post[0]->ID )
    );
	
	    return $latest_post . $prev;
    }
  else{
    $prev = sprintf(
        '<a class="previous-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $post ),
        $post->post_title
    );

 $latest_post = get_posts( 'numberposts=1&order=ASC' );

    $latest_post = sprintf(
        '<a class="latest-post" href="%1$s" title="%2$s"></a>',
        get_permalink( $latest_post[0]->ID ),
        get_the_title( $latest_post[0]->ID )
    );
	
    return $latest_post . $prev;
  }
}, 10, 4 );

Thanks!