Device Trust Issues

Under Device Management >> Devices >> (local device name) >> Device Connectivity, have you configured your failover network to use the interface you are trying use? Also, you say you are going over a WAN, correct? Do your two devices have management address defined that could be in the same L2 network? That could make them think they share a L2 domain and won't try to route to exchange certs. Also, make sure you don't have a gateway defined on your management network if you don't want to use it. Lastly, to complete the device trust you will need both 22, 443, and 4353 open between the two. Lastly, have you changed you httpd SSL settings at all?