blank white page when post/update/change option etc

Your function to call the sidebar “needs to be called” and also requires an id and should be in this format:

add_action( 'widgets_init', 'your_custom_sidebar' );

function your_custom_sidebar() {
    register_sidebar( array(
        'name'          => __( 'Footer Sidebar', 'your_theme_lang' ),
        'id'            => 'footer-sidebar',
        'description'   => __( 'Some description', 'your_theme_lang' ),
        'before_widget' => '<div class="col-md-3 col-sm-6 footer-col">',
        'after_widget'  => '</div>',
        'before_title'  => '<div class="logofooter">',
        'after_title'   => '</div><ul class="footer-ul">',
    ) );
}