Sometimes the ovs has two same vxlan-gpe ports ,one port is effective and another port number is null. For example :

[root@wlz-controller ~]# ovs-vsctl show
e5d7e63c-0c4a-4f0e-b0db-d3441d02c7c9
Manager "tcp:172.23.27.12:6640"
Bridge br-int
Controller "tcp:172.23.27.12:6653"
fail_mode: secure
Port "bond0"
Interface "bond0"
Port veth_br
Interface veth_br
Port "qosoutveth1"
Interface "qosoutveth1"
error: "could not open network device qosoutveth1 (No such device)"
Port "tun162d5c0de6a"
Interface "tun162d5c0de6a"
type: vxlan
options: {exts=gpe, key=flow, local_ip="10.0.1.91", remote_ip=flow}
Port br-int
Interface br-int
type: internal
Port "tap1e436556-5f"
Interface "tap1e436556-5f"
type: internal
Port "tapb1f58ae4-7c"
Interface "tapb1f58ae4-7c"
type: internal
Port "enp1s0f1"
Interface "enp1s0f1"
Port "tun6f0e9979c0b"
Interface "tun6f0e9979c0b"
type: vxlan
options: {exts=gpe, key=flow, local_ip="10.0.1.91", remote_ip=flow}

When sfc gert the egress vxlan-gpe port, it maybe get the null port. As a result , the flow table is wrong.