It's possible that a device send router a packet with mac address set to all zero and with a normal IP address. Perhaps the IP address is set by the device on its own. That makes sense.

Can you see any information in the DHCP list of the router?

@maclighter 1. The WiFi signal strength of 5GHz and 6GHz you said before is not so good. As you can see at -67 dBm Very Good Minimum signal strength for applications that require very reliable,...

@Costas-D Seems a new product PGW2440 KIT has been released recently that supports EasyMesh for fast roaming. In the case of your non-TP router supporting EasyMesh, you may choose this KIT. There are...

I am quite curious about what guide or manual have you seen.

@Domenico-jpf Hi, there. Have you seen the Quick Installation Guide? WAN and LAN you refer to appear beside the router ports.