Hello.
It’s good that it works a little more.
I think you may need to connect your wifi radios to your new VLAN6 interface.
It may be that the wifi radios are still connected to the normal WAN (eth0.2 I think) and that interface you don’t use anymore.
Luci>Network>Interfaces>your new wan (eth0.6) click Edit >Physical Settings and select Bridge. Put eth0.6 with your wifi radios (wlan0, wlan1 etc) as in the picture below.
It may be that your luci is different, mine is 19.07, but it has the same functions that you will find in yours.
I don’t have this setup, I just put it the way you can see what it’s like more or less.
