Hi… Unfortunately, there have been several recent reports of this feature failing—gradually congregating over in @ben_h’s subthread, 
:
https://community.fly.io/t/static-egress-ips-for-machines/22004/37
It might help to post your FLY_REGION and the output of traceroute icanhazip.com there.
(I get 5 lines for the latter, from an ewr machine with a default egress IP.)