Description of problem:
Executing these commands in the same transaction no longer works. ovn-nbctl complains:

[root@ovn-control-plane ~]# ovn-nbctl lr-nat-list GR_`hostname`
TYPE             EXTERNAL_IP        EXTERNAL_PORT    LOGICAL_IP            EXTERNAL_MAC         LOGICAL_PORT
snat             172.18.0.3                          10.244.0.0/16
[root@ovn-control-plane ~]# ovn-nbctl lr-nat-del GR_`hostname` snat 10.244.0.0/16 -- lr-nat-add GR_`hostname` snat 172.18.0.3 10.244.0.0/16
ovn-nbctl: 172.18.0.3, 10.244.0.0/16: a NAT with this external_ip and logical_ip already exists
[root@ovn-control-plane ~]# rpm -qa | grep ovn
ovn-20.12.0-25.fc33.x86_64
ovn-central-20.12.0-25.fc33.x86_64
ovn-host-20.12.0-25.fc33.x86_64
ovn-vtep-20.12.0-25.fc33.x86_64
[root@ovn-control-plane ~]# rpm -qa | grep openvs
openvswitch-2.15.0-1.fc33.x86_64
python3-openvswitch-2.15.0-1.fc33.x86_64


This used to work in previous versions. As Numan found the root cause looks to be:
https://github.com/ovn-org/ovn/commit/278ebb999411920206980f6b1b8c9b2d0b69d299