Raspberry Pi: Interface connection status not being updated mwan3

I am trying to use Raspberry Pi 4B with TPLINK TLSG108E smart switch, and using VLANs I am trying to create 2 WAN interfaces and make a failover setup using mwan3.

With a normal 21.02 release, or with @anon50098793 's custom builds, the router does to fall to the failover WAN interface, despite configuring VLAN properly.

In my setup, WAN is the main internet source and WANB is the failover source (a 4G connection).

When WAN is disconnected physically, i.e. when I pull the plug out from the smart switch , mwan3 detects it properly, but internet does not switch to WANB unless I click RESTART in the 'Interfaces' page, which is when the WANB is used.

But the same problem does not happen if I stop the WAN interface manually from 'Interfaces' page.

What could be the problem?

mwan3 status; cat /etc/config/network; cat /etc/config/mwan3
(remove/alter any usernames/passwords/macaddrs/personal-public-ip present)