Hi Jens -
I've verified that the system time is correct. My local machines are in California, and they work just fine.
I've verified with my network provider in Montreal that it's just broken inside our network provider. I don't yet know what's changed, and I'll update here when I do. However, since it's Google returning the response, I'm assuming something in App Engine is being too restrictive? Please note that the same problem is occurring on the Google Play publisher's console, so if that's running on AppEngine as well, that would make sense.
- Jordan