From what I can see the plugin script is moved to the footer, while the initialization is still in the header. I'm guessing it's either a minify/cache plugin doing that.
I think I have a solution, but a minor change must be made in one of the plugin files. I will write down the steps below, if you can't do it, feel free to add temporary FTP details to your ticket, and I will do it for you:
1. Make sure to have site back-up, just in case anything goes wrong.
2. Open up the wp-content\plugins\related-posts-pro\includes\hooks.php file on your server.
3. Scroll to line 63, which should be this: