Global Payments Hosted Payment Page Integration - sandbox and prod POSTs back to merchantUrl delays

I'm running our Hosted Payment Page integration the same as the official js lib:

https://github.com/globalpayments/rxp-js/blob/master/examples/hpp/process-a-payment-embedded-autoload-callback.html

All is good except this bit is very slow for the response to come back to our side with the approved/failed transaction:

https://github.com/globalpayments/rxp-js/blob/9909985b96ab5ed945614affad5f3739827f956b/examples/hpp/process-a-payment-embedded-autoload-callback.html#L16

e.g. The form gets presented, you enter your card details and click submit (on HPP) and then the 3D secure shows, does it's thing but around 4 mins later the result come back within the answer line (the above link, line 16). I'm not sure why it's so slow. Sandbox and Production are the same.

I'm opening a support case anyway, but if anyone has any ideas.

Thanks, Gavin.

Was the firewall on the box blocking https / port 443 from the public. Obviously the libs do something. All was instant when off.