Public custom VLAN not working on Fiber internet ICX 6610

[prasant_chettri]

I will be decommissioning and removing copper connection in couple of weeks. Instead of doing cutover migration using eth 0. I decided to setup eth4 for Fiber and with the help of support team I set the interface for external network with new public IP and setup it up as primary interface on a failover setting. so all DNS and policy that uses will continue using copper and gradually modify policy and 1to1 NAT and SNAT.
I have brocade 6610 layer three switch which has vlan 2001 for public ethernet. Copper port on switch was set to dual-mode on 2001 only and did not have association with default vlan 1.
While I was trying to create fiber with similar switch configuration I ended up setting fiber dual-mode with vlan membership of 2001 (tab), 1 and 200. I was able to remove vlan 200 which did not cause any issue but as soon as I remove vlan 1 and set dual mode 2001 only interface fails which is exactly same as copper. Not sure if switch need to be rebooted to fix it. But again as soon as I put it back on 1 and 2001 with dual mode it works fine so I assume firewall is seeing change from switch which means it should not require reboot to trickle the change.
Not sure why it does not work when I only try to associate to 2001 vlan which is set for public gateway. it is working fine on copper but fiber only works when traffic is routed from default vlan 1. Default vlan 1 is not best recommended vlan for any interface