addthis_below_content filter doesn't work anymore

Hello,

I have a code added to addthis_below_content filter, so on Single post pages I’m attaching ‘Share this article’ text before the share buttons, like so:

add_filter( 'addthis_below_content', 'custom_addthis_share_buttons_content' );
function custom_addthis_share_buttons_content( $content ) {
	if ( is_single() ) {
		$content = '<div id="addthis-single-post">' .
						'<span>Share this article:</span>' .
						$content .
						'<div class="fix"></div>'.
					'</div>';
	}
	return $content;
}

After upgrading to latest version of plugin 3.5.10 it stopped working and I don’t understand why.

Also, when setting up custom icons, you used to be able to see them, now they are displayed as red crosses.

Please let me know why addthis_below_content filter might not be working anymore.

https://wordpress.org/plugins/addthis/