My last code update:

My pre_get_posts:

add_action( 'pre_get_posts', function ( $query ) {
    if (!is_admin() && $query->is_main_query() && $query->is_category())
        $query->set( 'posts_per_page', 11 );
});

Currently I'm facing a really strange problem I can't seem to fix normally. I've using pagination on my category pages. I've got a 'News' category with some sub categories. One sub category is 'MVO nieuws'.

When I visit '/mvo-nieuws' the pagination is working (showing an older posts link).

if ($paged) : ?>
    <nav class="page-nav archive">

        <?php if ($prev = get_previous_posts_link()) : ?>
            <div class="alignleft">
                <span class="fo icons-angle-circled-left"></span>
                <span><?php previous_posts_link( 'Nieuwe berichten' ); ?></span>
            </div>
        <?php endif;

        if ($next = next_posts($listPosts->max_num_pages, false)) : ?>
            <div class="alignright">
                <span>
                    <a href="<?= $next; ?>">Oudere berichten</a>
                </span>
                <span class="fo icons-angle-circled-right"></span>
            </div>
        <?php endif; ?>

    </nav>
<?php endif; ?>

The pagination is forwarding to '/mvo-nieuws/page/2', but that page couldn't be found. I'll found out this is because its a subcategory of 'News', but I don't know why this seems to be a problem.

I've removed the category as a subcategory and now it's working. All my other primary categories are also working fine, but the subcategories are facing this problem.

My permalink settings are: '/%category%/%postname%/'. Hopefully anyone can help me out, thanks in forward!

Currently I'm facing a really strange problem I can't seem to fix normally. I've using pagination on my category pages. I've got a 'News' category with some sub categories. One sub category is 'MVO nieuws'.

When I visit '/mvo-nieuws' the pagination is working (showing an older posts link).

if ($paged) : ?>
    <nav class="page-nav archive">

        <?php if ($prev = get_previous_posts_link()) : ?>
            <div class="alignleft">
                <span class="fo icons-angle-circled-left"></span>
                <span><?php previous_posts_link( 'Nieuwe berichten' ); ?></span>
            </div>
        <?php endif;

        if ($next = next_posts($listPosts->max_num_pages, false)) : ?>
            <div class="alignright">
                <span>
                    <a href="<?= $next; ?>">Oudere berichten</a>
                </span>
                <span class="fo icons-angle-circled-right"></span>
            </div>
        <?php endif; ?>

    </nav>
<?php endif; ?>

The pagination is forwarding to '/mvo-nieuws/page/2', but that page couldn't be found. I'll found out this is because its a subcategory of 'News', but I don't know why this seems to be a problem.

I've removed the category as a subcategory and now it's working. All my other primary categories are also working fine, but the subcategories are facing this problem.

My permalink settings are: '/%category%/%postname%/'. Hopefully anyone can help me out, thanks in forward!

EDIT After Pieter Goosens his comment I thought it would be handy if you guys could see my query.

$cat = get_query_var('cat');
$category = get_category($cat);

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$listArgs = array(
    'cat' => $category->term_id,
    'paged' => $paged,
    'posts_per_page' => 11
);

$listPosts = new WP_Query($listArgs);

while ($listPosts->have_posts()) :
    $row++;
    $listPosts->the_post(); 
endwhile;

I'll hope this can help solve my problem.