Why is my custom post type slider only displaying the latest slide?

after a search throughout the already asked questions I couldn't come to a solution to my problem, this one is the closest I found: My custom post type displays the [latest post]

I had a slider built into the homepage, but I have noticed that after a while of it working fine, it now only displays the latest post type.

Here is the current code for the slider:

div class="half slide-container"
            ul class="slider"
                ?php
                    $slides = get_posts( array(
                        'numberposts' = 6,
                        'post_type' = 'slides',
                        'orderby' = 'post_date'
                    ) );
                    foreach( $slides as $post ) :
                        setup_postdata( $post );
                        $args = array(
                            'post_type' = 'attachment',
                            'numberposts' = null,
                            'post_status' = null,
                            'orderby' = 'post_date',
                            'order' = 'ASC',
                            'post_parent' = $post-ID
                        ); 
                    $attachments = get_posts( $args );
                ?
                    li data-background="http://www.serps.co.uk/cdn/PG/background14.png"
                        ?php the_content(  ); ?
                    /li
                ?php endforeach; ?
            /ul
        /div

I'm relatively new to .php, but I thought I had spotted a couple of syntax errors but the slider still remained broken.

I changed it to this to no avail:

div class="half slide-container"
            ul class="slider"
                ?php
                    $slides = get_posts( array(
                        'numberposts' = '3',
                        'post_type' = 'slides',
                        'orderby' = 'post_date'
                    ) );
                    foreach( $slides as $post ) :
                        setup_postdata( $post );
                        $args = array(
                            'post_type' = 'attachment',
                            'numberposts' = '3',
                            'post_status' = 'publish',
                            'orderby' = 'post_date',
                            'order' = 'ASC',
                            'post_parent' = $post-ID
                        ); 
                    $attachments = get_posts( $args );
                ?
                    li data-background="http://www.serps.co.uk/cdn/PG/background14.png"
                        ?php the_content(  ); ?
                    /li
                ?php endforeach; ?
            /ul
        /div

You can view this live on the website here: Polesworth Garage