I believe this is not the same issue as https://bugs.launchpad.net/neutron/+bug/1571113, here is what I got before the node failure and everything looks good:
wichita-citron:/opt/openstack # ip netns exec snat-c83cfa28-685e-4363-859e-18400b27ee4f ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
161: qg-97c348f7-d9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default 
    link/ether fa:16:3e:9f:f9:cf brd ff:ff:ff:ff:ff:ff
    inet 10.240.127.2/32 scope global qg-97c348f7-d9
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fe9f:f9cf/64 scope link 
       valid_lft forever preferred_lft forever
163: sg-019439c9-de: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default 
    link/ether fa:16:3e:c2:7d:2c brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.3/24 brd 192.168.1.255 scope global sg-019439c9-de
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fec2:7d2c/64 scope link 
       valid_lft forever preferred_lft forever

wichita-citron:/opt/openstack # neutron router-port-list admin-router -c fixed_ips
+-------------------------------------------------------------------------------------+
| fixed_ips                                                                           |
+-------------------------------------------------------------------------------------+
| {"subnet_id": "3c0d5091-1349-4b42-aede-c62717c83b72", "ip_address": "192.168.1.3"}  |
| {"subnet_id": "3c0d5091-1349-4b42-aede-c62717c83b72", "ip_address": "192.168.1.1"}  |
| {"subnet_id": "5e0665ec-020b-4626-98c0-29490f675c7d", "ip_address": "10.240.127.2"} |
+-------------------------------------------------------------------------------------+

Then I reboot this active neutron router node which has the snat namespace on it. The failover happened and I see snat namespace was created on the other network node. The router-port list still give me the right result as below, only the "sg-019439c9-de" interface is disappeared from the snat namespace

honolulu-citron:/opt/openstack # neutron router-port-list admin-router -c fixed_ips
+-------------------------------------------------------------------------------------+
| fixed_ips                                                                           |
+-------------------------------------------------------------------------------------+
| {"subnet_id": "3c0d5091-1349-4b42-aede-c62717c83b72", "ip_address": "192.168.1.3"}  |
| {"subnet_id": "3c0d5091-1349-4b42-aede-c62717c83b72", "ip_address": "192.168.1.1"}  |
| {"subnet_id": "5e0665ec-020b-4626-98c0-29490f675c7d", "ip_address": "10.240.127.2"} |
+-------------------------------------------------------------------------------------+

honolulu-citron:/opt/openstack # ip netns exec snat-c83cfa28-685e-4363-859e-18400b27ee4f ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
261: qg-97c348f7-d9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default 
    link/ether fa:16:3e:9f:f9:cf brd ff:ff:ff:ff:ff:ff
    inet 10.240.127.2/25 brd 10.240.127.127 scope global qg-97c348f7-d9
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fe9f:f9cf/64 scope link 
       valid_lft forever preferred_lft forever
honolulu-citron:/opt/openstack #