I'm not familiar with this topic, but I stumbled upon the following thread yesterday:
I know that it doesn't fully cover your problem, but maybe you can find a hint on the solution there? At first glance, I would try to add the options
vlan_tagged_interface 'br-switch'
vlan_naming '1'
to your wifi-iface section as explained in the wpa_psk_file section of the documentation.