Further details, there do seem to be issues with the ssl cert. Doug, may we bother you to take a peek?
https://www.ssllabs.com/ssltest/anal...nsairforce.net
In particular, I believe the issue is the Cert chain is missing the "let's encrypt" intermediate cert. To fix this I believe you need to add it to your apache config:
SSLCertificateChainFile /etc/letsencrypt/lets-encrypt-x1-cross-signed.pem