Styling text and images in the_content()

I think the problem is the way you use the foreach with HTML inside. I usually use this way, so try perhaps to modify your code like this :

<?php

if (have_posts()) {
    while (have_posts()) {
        the_post();
        the_content();
        //  get_template_part( 'template-parts/content','article' );
        $args = array(
            'post_type' => 'attachment',
            'numberposts' => -1,
            'post_status' => null,
            'post_parent' => $post->ID
        );
    }
    $attachments = get_posts($args);
    if ($attachments) {
        foreach ($attachments as $attachment) : ?>

            <div class="img-box clearfix detect-inview-2 inview">
                <div class="item loaded">
                    <img src="<?php echo wp_get_attachment_url($attachment->ID); ?>" />
                </div>
            </div>

        <?php endforeach;
    }
}