Thanks for responding. In the mean time I did resolve the "--remote-cert-tls server" issue by using certificated generated with quick-RSA. Though I must say, as RUTX50 is considered a professional level device, the certificates which are generated by the device should also support extended keys following RFC 3280 TLS rules.
Regarding my first observation, requiring a restart of the server. This has nothing to do with the internet connection. Internet connection is stable. It happens when the ovpn server remains active for a few days without any client connecting to it. For example. Ovpn server is running for 4 days, then on the 5th day a connection attempt is made, that connection is not accepted. Workaround is to re-start the server, it then starts accepting connections again. Quite weird.