I mean you no offense
I did set the local address using openvpn-option "--local 192.168.21.1". I have to do it this way since the CLI won't commit the local-host attribute when the mode is set to server. The NAT is so that I don't need to care about the outside IP address and works just fine.
This is, however, just a workaround. The kernel being used in the Edge Router OS doesn't fully support mapping IPv4 addresses on an interface that also has IPv6 addresses when using an unbound UDP socket. As a result, the openvpn process is unable to respond properly. Binding to an IPv4 address creates an IPv4 socket so things will work, but that prevents IPv6 connections to the same interface. In my configuration, I need to allow both IPv4 and IPv6 connections.