There are only 2 posts on that page, so there’s not a lot to go on here, but it looks like there is not enough text to warrant a Read More button for the second post.
By default, WordPress has an excerpt length of 55 words (looks like that’s in effect on your site). The second post isn’t long enough to have an excerpt so the full post is shown.
You can change the number of words in the excerpt to something shorter. Add this code to your theme’s functions.php file:
/**
* Filter the except length to 20 words.
*
* @param int $length Excerpt length.
* @return int (Maybe) modified excerpt length.
*/
function wpse240108_custom_excerpt_length( $length ) {
return 20;
}
add_filter( 'excerpt_length', 'wpse240108_custom_excerpt_length', 999 );
Alternatively, you can add a <!--more--> tag within the content generate your own excerpt rather than relying on WordPress to generate the excerpt.