I get the login page when I go through my 18.104.22.168. You don't even get that far?
It looks a timeout issue where the gateway doesn't receive a response. Do you get a 60 second delay beofre the error displays?
We get the error with 3 or 4 seconds. Works every time if we bypass!
Sounds like a good one to work with support on and perhaps have a packet capture and policy trace taken to speed up the analysis process.