You had a looping issue in shortcode-button.php

When activating the plugin it produced a Fatal Error. What happened is you had a function shortcode_button() already declared and it was looping and trying to create it again. I fixed it with the code below.

1.Install plugin
2.Edit plugin file shortcode-button.php with code below
3 Update

if(!function_exists('shortcode_button'))
{
   function shortcode_button($atts, $content = null){
	$content = trim(do_shortcode(shortcode_unautop($content)));
	extract(shortcode_atts(array("mode" => 'link', "href" => 'http://'), $atts));
	switch ($mode) {
		case 'down':
			return '<span class="but-down"><a href="'.$href.'" target="_blank"><span>'.$content.'</span></a></span>';
		break;

		case 'heart':
			return '<span class="but-heart"><a href="'.$href.'" target="_blank"><span>'.$content.'</span></a></span>';
		break;

		case 'link':
			return '<span class="but-link"><a href="'.$href.'" target="_blank"><span>'.$content.'</span></a></span>';
		break;

		case 'doc':
			return '<span class="but-document"><a href="'.$href.'" target="_blank"><span>'.$content.'</span></a></span>';
		break;

		default:
			return '<a href="'.$href.'" target="_blank">'.$content.'</a>';
		break;
	}
    }
}

https://ww.wp.xz.cn/plugins/shortcode-button/