The SSL Checking service did indeed point out the error. I will admit to my own stupidity on this one. We're using Elastic Load Balancing on

*.example.co

ELB had only our other SSL Cert configured and not our new one. Darn it. We don't use ELB for example.co because you can't CNAME the root domain so that hit our server directly and of course with the tweaked config worked fine.

Now I've added our new SSL cert to ELB, both urls work fine. Thanks very much for all of your assistance working through this, although ultimately it wasn't all Nginx.

Cheers.