I am experiencing the same issue with Google Home. Just recently as well.
In addition to HTTP error 408, I'm also receiving a "Devices are not available" message as well. I can control things locally just fine. Seems to be related to the portal access.
@Jimbo
Any chance this could be revisited? Being able to send Google Home commands from an ISY would be a great feature. I can think of a million things I'd like to tap into with that functionality. This is exactly what I'm looking for!