Has anyone got comments or observations about the built-in OpenVPN Server on Spark Smart Modem 2 (FWA)? 

I found that sometimes after intentional client disconnection the Server (UDP mode) would not accept connections even from another device. Turning the power off/on to restart the Smart Modem 2 did not help. The VPN Server would be running again after the power off/on, but it appears that the Server process was not fully terminated or cleanly re-initialised. The only solution seemed to be to Stop & re-Start the Server process itself which cannot be done remotely. 

As a work-around I inserted "explicit-exit-notify 5" into the client OpenVPN Connect .ovpn files, which so far seems to have eliminated the lockouts. (NB that command has different effects for UDP/TCP and client/server). The apparent lack of ability to reset the OpenVPN Server by a power-off/on, for example by a power-outlet automatic timer switch in case of a lockout when there is no-one in attendance at the Smart Modem 2's location, is still potentially a problem.