normally configuration hierarchy will be there.
Global config -> override by WLAN config -> override by AP Group config -> override by AAA
I am sure even WLAN map to vlan90 on WLAN config level, under AP group you might map it to vlan30 interface. So AP group config takes precedence and users will get vlan 30 IPs.
In flexconnect local switching scenario, WLAN map interface does not matter as capwap data traffic does not come to the controller. So you can map WLAN to dummy interface or mgt interface for simplicity.
HTH
Rasika
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