OK, thank you. There are two things that will cause a flap: 1. 100% CPU spikes, but these, in my experience, flap all the active interfaces 2. Energy Efficient Ethernet being enabled on a non-Meraki switch or router. This is a known issue.    What is the make/model of the switch you are using between the ISP and the MX?  ... View more

From the documentation, this may take some time to update: https://documentation.meraki.com/General_Administration/Cross-Platform_Content/Device_Showing_an_Incorrect_Public_IP   Have you tried performing a hard reset? ... View more