When you see two routes, within the same network, assigned to both ports… that is a problem.
220.127.116.11/28 dev eth2 proto kernel scope link src 18.104.22.168
22.214.171.124/29 dev eth1 proto kernel scope link src 126.96.36.199
This lead me to look at anything that could add interface addresses to the system, Interfaces, Secondary IPs, Site2Site and NAT mappings.
Here is what I found for NAT mappings:
A one-to-one mapping rule with WAN2 addressing, assigned to WAN1.
That was causing the WAN2 to flap as the system could not determine how to route WAN2 traffic as both interfaces had this subnet assigned.
As soon as I changed this rule to WAN2, the port came up and no further problems.