Me too. If anyone figures this out, I'd love to hear more.
I believe all my DNS records look fine, and I have the domain ownership set correctly with GAE. Not sure what else I can change to get it working.
I checked the DNS records and the CNAME, A, AAAA records of all the domains match exactly what is shown on the admin console.
Thanks for the support! And thanks for all the good work on AppEngine!
And thanks to other commenters too!