Posts per page option not working

also this is the way im showing the posts:

function latest_posts_mansory(){

$output = '';

$this_category = get_category( get_query_var( 'cat' ) );
$cat_id = $this_category->cat_ID;
$args = array( 'post_status' => 'publish' );
$args['showposts'] = 12;
if (is_author()) {
$args['author'] = get_the_author_meta('ID');
} else {
$args['category'] = $cat_id;
}
$recent_posts = wp_get_recent_posts( $args );
$num_posts = count($recent_posts);
$curtitle = get_category_parents( get_query_var('cat') , false , ' - ' );
if (!is_author()) {
$output .= '<div class="section_title underline" id="section-title-5314721809a17" style="border-color: #dddddd;"><span class="title">'.substr($curtitle , 0, -2).'</span></div>';
} else {
$output .= '<div class="section_title underline" id="section-title-5314721809a17" style="border-color: #dddddd;"><span class="title">Προβολ? ?ρθρων</span></div>';
}
$output .= '<div class="post_list masonry isotope" style="display: block; position: relative; overflow: hidden; height:494px;">';
$j=0;
if ($num_posts == 0 && is_author()){
$output .='<div class="no results" style="text-align:center;position: inherit;" align="center"><h5 ALIGN="CENTER">Δεν υπ?ρχουν ?ρθρα απ\'τον συγκεκριμ?νο συντ?κτη</h5></div>';
}elseif ($num_posts == 0){
$output .='<div class="no results" style="text-align:center;position: inherit;" align="center"><h5 ALIGN="CENTER">Δεν υπ?ρχουν ?ρθρα σε αυτ?ν την κατηγορ?α</h5></div>';
}else{
for ($i=0; $i<$num_posts; $i++){

$recent_posts_usage = $recent_posts[$i]['ID'];
$this_ID = $recent_posts[$i]['ID'];
$post_class = join(" ", get_post_class('', $this_ID));
$this_title = get_the_title ($this_ID);
$category = get_the_category ($this_ID);
$this_category = $category[0]->cat_name;
$this_thumb = get_the_post_thumbnail( $this_ID, 'medium');
$this_permalink = get_permalink($this_ID);
$page_data = get_page( $this_ID );
$excerpt = T2T_Toolkit::truncate_string(apply_filters('the_content', strip_tags($page_data->post_content)), 200);

$output .= '<div class="callout_box with_post one_fourth isotope-item';
if($j==3){
$output .= ' column_last';
$j=0;
} else {
$j++;
}
$output .= '" style="position: absolute; left: 0px; top: 0px; -webkit-transform: translate3d(476px, 0px, 0px);">';
$output .= '<article id="post-'.$this_ID.'" class="'.$post_class.'">';
$output .= '	<a href="'.$this_permalink.'"> 	'.$this_thumb.' </a>';
$output .= '<div class="callout_box_content">';
$output .= '<h3>    <a href="'.$this_permalink.'">'.$this_title.' </a></h3>';
$output .= $excerpt;
$output .='</div>';
$output .='</div>';
$output .='</article>';
}
}
$output .='</div>';
return $output;
}

add_shortcode('show_latest_posts_mansory', 'latest_posts_mansory');

seems to be fixed
– was it caused by your cache plugin?

no it was the wp_get_recent_posts command. i should never use those again and i will use only the main functions and queries like WP_Query wordpress usually use.
This is the new function that is working:

$output = '';
			$this_category = get_category( get_query_var( 'cat' ) );
			$cat_id = $this_category->cat_ID;
			$args = array( 'post_status' => 'publish' );
			if (is_author()) {
						$args['author'] = get_the_author_meta('ID');
			} else {
						$args['cat'] = $cat_id;
			}
			$args['paged'] = get_query_var( 'paged' );
			$curtitle = get_category_parents( get_query_var('cat') , false , ' - ' );

			//echo headers
			if (!is_author()) {
						$output .= '<div class="section_title underline" id="section-title-5314721809a17" style="border-color: #dddddd;"><span class="title">'.substr($curtitle , 0, -2).'</span></div>';
			} else {
						$output .= '<div class="section_title underline" id="section-title-5314721809a17" style="border-color: #dddddd;"><span class="title">Προβολ? ?ρθρων</span></div>';
			}
			$output .= '<div class="post_list masonry isotope" style="display: block; position: relative; overflow: hidden; height:494px;">';

			$recent_posts = new WP_Query( $args );
			if ( $recent_posts->have_posts() ) {
			    while ( $recent_posts->have_posts() ) {
			        $recent_posts->the_post();
			        // do stuff

							$num_posts = count($recent_posts);

							//get ID,title,permalink etc
							$j=0;
							$recent_posts_usage = get_the_ID();
							$this_ID = get_the_ID();
							$post_class = join(" ", get_post_class('', $this_ID));
							$this_title = get_the_title ();
							$category = get_the_category ();
							$this_category = $category[0]->cat_name;
							$this_thumb = get_the_post_thumbnail( $this_ID, 'medium');
							$this_permalink = get_the_permalink();
							$page_data = get_page( $this_ID );
							$excerpt = T2T_Toolkit::truncate_string(apply_filters('the_content', strip_tags($page_data->post_content)), 200);

							//echo content
							$output .= '<div class="callout_box with_post one_fourth isotope-item';
							if($j==3){
										$output .= ' column_last';
										$j=0;
							} else {
										$j++;
							}
							$output .= '" style="position: absolute; left: 0px; top: 0px; -webkit-transform: translate3d(476px, 0px, 0px);">';
							$output .= '<article id="post-'.$this_ID.'" class="'.$post_class.'">';
							$output .= '	<a href="'.$this_permalink.'"> 	'.$this_thumb.' </a>';
							$output .= '<div class="callout_box_content">';
							$output .= '<h3>    <a href="'.$this_permalink.'">'.$this_title.' </a></h3>';
							$output .= $excerpt;
							$output .='</div>';
							$output .='</article>';
							$output .='</div>';

			    }
			    wp_reset_postdata();
			} else {
			    	// none were found
						if (is_author()){
									$output .='<div class="no results" style="text-align:center;position: inherit;" align="center"><h5 ALIGN="CENTER">Δεν υπ?ρχουν ?ρθρα απ\'τον συγκεκριμ?νο συντ?κτη</h5></div>';
						}else{
									$output .='<div class="no results" style="text-align:center;position: inherit;" align="center"><h5 ALIGN="CENTER">Δεν υπ?ρχουν ?ρθρα σε αυτ?ν την κατηγορ?α</h5></div>';
						}
			}

			$output .='</div>';
			return $output;