I have Gigabit fiber and every now and then the connection goes dead. When I reboot the router and the ONT, everything works again but I always find that the new IP address comes from a different block (it doesn't happen if I reboot at other times). I'm guessing that when Sonic changes setting on their end my router doesn't update properly.
Typically the IP switches between 18.104.22.168/16 and 22.214.171.124/16, but last night, as the the connection died again and I restarted everything again, the new IP was on 126.96.36.199/17.
Stranger still, a reverse DNS query tells me that this block is called *.static.sonic.net.
Is Sonic experimenting with static IPs on fiber?
That would be excellent news!