pfSense

explicit-exit-notify looks like it can greatly speed up recovery time on OpenVPN process restarts and potentially HA server installations.

From https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage

       --explicit-exit-notify [n]
              In UDP client mode or point-to-point mode, send server/peer an
              exit notification if tunnel is restarted or OpenVPN process is
              exited.  In client mode, on exit/restart, this option will tell
              the server to immediately close its client instance object
              rather than waiting for a timeout.  The n parameter (default=1)
              controls the maximum number of attempts that the client will try
              to resend the exit notification message.

              In UDP server mode, send RESTART control channel command to
              connected clients. The n parameter (default=1) controls client
              behavior. With n = 1 client will attempt to reconnect to the
              same server, with n = 2 client will advance to the next server.

              OpenVPN will not send any exit notifications unless this option
              is enabled.