[solved] undefined $post->ID in WP_Query()

Hello everyone, I am facing weird error in my website I can see this error 

Warning: Undefined variable $post in /customers/2/5/e/mastratec.com/httpd.www/wp-content/themes/salient-child/skills-section.php on line 21

Warning: Attempt to read property "ID" on null in /customers/2/5/e/mastratec.com/httpd.www/wp-content/themes/salient-child/skills-section.php on line 21

the file looks like 

<?php 
	$args = [
		'post_type' => 'skills',
		'status' => 'published',
		'orderby' => 'date', 
		'order' => 'ASC',
		'posts_per_page' => -1,
	];
	$count = 0;
	$posts = new WP_Query( $args );
	if( $posts->have_posts() ) :
		?>
 <div class="skills_container">
		<?php 
		$count = 1 ;
		while($posts->have_posts()):
			$posts->the_post();
			?>
				<div class="post">
 <div class="inner_post">
 <?php if(get_the_post_thumbnail_url($post->ID)){ ?>
 <img src="<?php echo get_the_post_thumbnail_url($post->ID); ?>" alt="Image">
 <?php } ?>
 <div class="details">
 <h4><?php the_title(); ?></h4>
 </div>
 </div>
				</div>
			<?php
			if($count % 6 == 0){
				echo "</div> <div class='skills_container'>";
			}
			$count++ ;
		endwhile;
	else:
		echo "<h3 style='text-align: center;'> No posts to show </h3>";
	endif;
?>

This is the first time to see this error however that code is working fine on another server,
Please help