On a router where a client is connected continuously (and that is reflected in OpenVPN status: it's not disconnecting/reconnecting), the system log shows about 20 lines of essentially redunctant and not very useful activity for the client every hour. The info is very similar to, but slightly different from, what's recorded upon initial connection.
I'm guessing that it ties to this default:
Short of increasing that (adjustments on both the client and the server), I wonder if there's a way of just suppressing the openvpn daemon notices for this renegotiation.–reneg-sec n
Renegotiate data channel key after n seconds (default=3600).