UAP AP Port Conf
General Conf: (you must disable this)
no vlan dot1q tag native
The management interface or SSID must not be tagged but all others must be for this to work.
Port Conf:
interface GigabitEthernet1/3 description WAP0 switchport trunk encapsulation dot1q switchport trunk native vlan <LAN Vlan> switchport trunk allowed vlan <LAN Vlan>,<GUEST Vlan> switchport mode trunk spanning-tree portfast trunk end
In the conf above the native vlan must also be listed in the "allowed vlan" conf line.
UBNT Controller: More info here https://help.ubnt.com/hc/en-us/articles/219654087-UniFi-Using-VLANs-with-UniFi-Wireless-Routing-Switching-Hardware#UAP