Forwarding traffic between two bridges won't work

That would be 6.

Nope, no managed switch in my net.

Anyway, this all doesn't matter, because the problem exists even without my custom vlan configuration, when I just try to forward between br-lan and wlan1-1.

I am not sure if it is connected, but sometimes the devices are not working well with low vlan ids.
Can you try to use higher Vids like this one here?

I changed vlan ids 2 and 3 to 200 and 300, respectively (vlan id 1 wasn't changed in the example). No visible effect.

As I said, the problem was already there when I hadn't bridged wlan1-1 with ethX.Y and was using only wlan1-1 with no mods to the switch config at all.

I am out of ideas unfortunately :frowning: