That's the issue I am having.
I have DHCP on my Windows Server 2016 Box (Private network) for Vlan1 and DHCP on the Meraki for Vlan2 for the Public/Guest.
When clients join the private Wifi (no lan specified on the Unifi) they get an IP from the Windows Server. When the clients join the public Wifi Vlan2, no DHCP.