Adam, In your case It is your server configuration …As mentioned before. SLP is working. SLP from loading.
Look at the screenshot and the error that is showing google tags built into your index.
Also, do you have referrers? Do you have just a browser key. Please read how to restrict your key. Currently it is not being blocked or restricted because I can clearly see it. I am guessing you have it in wrong spot or set up incorrectly for that customer
or if you do not restrict just add browser key