pfSense » pfSense Plus

The SIP phone, communicating through pfSense, stops working from time to time.

Checking the state table it shows that the NAT translation, only for the phone, is happening to an IP address 84.230.48.58 which doesn't exist on the pfSense (probably an old WAN IP address). The PPPoE interface uptime is couple of hours, which there was a WAN IP address change recently.
NAT for all other connections are OK.

The real WAN IP address is 87.97.33.xx but the SIP packets from the phone are translated to 84.230.48.58

After disconnecting the phone for two minutes the faulty state cleared from pfSense. After connecting the phone again a new state has been created and the NAT is now happening with the correct IP address, and the phone is working again.

Netgate SG-2440 24.03-RELEASE
Basic Vanilla setup with no additional packages installed like siproxd.
There is only one host communicate to this remote IP:Port.
There is no 1:1 NAT and port randomization is enabled.
There is no static port configured.

So far I experienced incorrect NAT issue, which causes a SIP phone to stop working, at three locations, each with different pfSense hardware (1100, 4200, SG-2440) and with different SIP phone make and models.
Very similar case to https://redmine.pfsense.org/issues/15535 (incorrect NAT) but here we can't say that "If you use NAT in such a way that it would try to make two connections use the same conflicting information, it will fail to create a NAT state and the second connection will egress without NAT." Here the packets don't egress without NAT, the NAT is happening, but to an IP address which doesn't exist on the pfSense.