LuCI interface down

Hello
I have a setup in which my openwrt and open MPTCP router are running on truenas. openMPTCP router is used for the bonding of cellular connection. The openwrt has 2 wan connection, wan1 the bonded cellular connection (dhcp private ip)from openMPTCP router and wan2 a fibre connection(static public ip).

PROBLEM:

i want to achieve failover between the wan1 and wan2. when i do testing the wan 1(bonded cellular) to wan2 (fiber ) works well. The other way around that is from wan 2 to wan1 also works. but the problem is when i manually disable wan2, i lose the interface access. Happens when the interface is accessed over a public ip.

ERROR:
XHR request timed out.

but when doing failover in a local network, i don't experience this issue with the LuCI interface.

HARDWARE SETUP:
1.Version: TrueNAS-SCALE-22.12.2
2. Motherboard: Supermicro X12SCZ-TLN4F/F
3. Onboard GPU: ASPEED AST2500
4. CPU: Intel XEON W-1250 / 6C/12T - 3,30GHz - MaxBoost: 4,7GHz / Intel UHD P630 / 80W
5. RAM: 16GB / ECC DDR4-3200 RAM / M391A2K43DB1-CWE
6. Storage: HDD SATA 6Gb/s - 20 TB - WD HC560 WUH722020BLE6L4 ; 64GB SATA-DOM - 68 TBW/3y - Supermicro SSD-DM064-SMCMVN1 ; SSD NVMe 2280 - 7. Samsung 980 - 500 GB - 300 TBW - MZ-V8V500BW

Any helps/suggestion would be really appreciated.
Thanks

it's a browser side issue, if I remember correctly.
https://forum.openwrt.org/search?q=XHR%20request%20timed%20out%20order%3Alatest

i have seen that similar issue with the browser and made the changes according to the other posts
setting keepalive = 0
but in my case, it didn't work. Still the issue persist