Kaspars, thanks for your assistance in getting me on the right path to solving the problem. It is truly appreciated. The problem ended up being that the wp_remote_post(); function actually adds slashes within the $_POST['request'] serialized array. A simple addition of stripslashes() around $_POST['reqeust'] around line 36 does the trick, like so:

$args = unserialize(stripslashes($_POST['request']));

All the best.