From Mist,

Wan Edge (left navbar), Wan Edge

site Wan Edge device list, lists an Public IP Address that not configured on device

IP address displayed in MIST is not configured on any device interface.

The IP listed on this screen is the public IP traffic is seen from Mist Cloud, most commonly when the SSR/Wan Edge device is connected though a NAT device.

This could be an Carrier-Grade NAT (CGNAT) or an upstream service provider firewall is translating the address before the traffic reaches the Mist cloud.