Was there a resolve for this? I have the same issue, logs "can not find any account forthe incoming call" every 2 minutes. I do not have a VOIP phone connected, but do have an NBN phone number. Are the logs anything to be concerned about?
Since your VoIP has a registered SIP, the device is logging that it can still receive an incoming call from an unknown source or destination and therefore did not accept the call hence the logs.
It shows the router is doing its job by blocking these rogue calls.