I have an RUT955 (RUT9XX_R_00.06.05.3) and try to configure an openvpn client.
It didn't start, so I checked the logging and it shows
daemon.err openvpn(client_EnergyNxt)[14273]: Options error: Unrecognized option or missing or extra parameter(s) in openvpn-client_Vpn.conf:25: tls_auth (2.4.5)
When checking the configuration there is an option with tls_auth, but this should be tls-auth (minus instead of underscore).