Thanks

	<?php do_action('sydney_after_header'); ?>

	<div class="sydney-hero-area">
		<?php sydney_slider_template(); ?>
		<div class="header-image">
			<?php sydney_header_overlay(); ?>     

    <img class="header-inner" src="<?php if(has_post_thumbnail($post->ID)){the_post_thumbnail();} else {header_image();} ?>" width="<?php echo esc_attr( get_custom_header()->width ); ?>" alt="<?php bloginfo('name'); ?>" title="<?php bloginfo('name'); ?>">
			
		</div>
		<?php sydney_header_video(); ?>

<?php do_action('sydney_after_header'); ?>

	<div class="sydney-hero-area">
		<?php sydney_slider_template(); ?>
		<div class="header-image">
			<?php sydney_header_overlay(); ?>     

    		<img class="header-inner" src="<?php if( has_post_thumbnail($post->ID) ) { echo get_the_post_thumbnail($post->ID); } else { header_image(); } ?>" width="<?php echo esc_attr( get_custom_header()->width ); ?>" alt="<?php bloginfo('name'); ?>" title="<?php bloginfo('name'); ?>">
			
		</div>
		<?php sydney_header_video(); ?>

and see if that does anything. You should also inspect your code in your browser to see what gets output each time. it helps troubleshoot things like this.