USG60 - VLAN-Configuration - No Product/Mac-Address/DNS on Network-Ping

Hi Community, 

now I've run out of ideas where to continue.

I've set-up some VLANs with own subnets. Everything works fine up to here. DHCP IP-Assignments works fine. But!

If I assign the LAN1 IP-Adress to a Wireless-Equipment then on an IP-Scan the IP-Adress, the network Name, Mac-Address, Product, Producer, DNS etc. all is present.

If I assign the same equipment to e.g. VLAN1 then on an IP-Scan a proper IP is assigned but  NO Name, Mac-Address, Product etc. is shown - it's stated as unknown.

A hint, a push in the right direction would be highly appreciated.

Thanks
Francesco