I would try turning off any stateful inspection you might have for the EISY via the PAN (Palo Alto). We're a PAN shop at work - and I know it will scrutinize traffic very much and sometimes tooo much. Since it's is unable to reach the internet it likely doesn't send the traffic out to the portal (guessing). So that would explain why when it's unable to ping the internet it stops trying to connect to the portal and not showing any traffic as well.
Since you can't reach the internet from the EISY - it obviously won't reach the UD Portal. Assuming you don't have similar issues with other devices on the network I would see how the traffic is any different - different rules? Different path? etc. I'm leaning towards the PAN getting in the way....