why it's like this?

please take a look at the image of my archive.

Why the "read more" buttons are looking different for different posts?

I used a custom snippet earlier to show the button.

this snippet is for adding "read more" despite using custom excerpt in the blog archive section:

add_filter( 'wp_trim_excerpt', 'tu_excerpt_metabox_more' );
function tu_excerpt_metabox_more( $excerpt ) {
$output = $excerpt;

if ( has_excerpt() ) {
$output = sprintf( '%1$s <p class="read-more-container"> Start Reading </p>',
$excerpt,
get_permalink()
);
}

return $output;
}

Note: I also cleared all my cache, the problem still remains.