DHCP client not listed in DHCP Server

[woni]

Hello, we use pfs 2.1 and have trouble with the DHCP Server.
We can see via CaptivePortal logged in users with a correct IP from the DHCP server range. But this client is not listed in Status -> DHCP-Server.
We have two LANs (192.168.8.0/24 and 192.168.4.0/24) with DHCP server configured. The CP is working with vouchers.
A further problem is, clients can connect sometimes and sometimes not over CP.

Any idea?