Problems with Guest WLAN

Hello together

We have set up a guest WLAN at a USG 110. This has always worked. Now we had to switch because of the telephone change a Lancom router in front of it. And since then the guest WLAN does not work anymore. Shortly to configure the Internet access: Zyxel: LAN1 = 192.168.9.250 WAN = 192.168.8.239 GW = 192.168.8.238 (= LAN1 Lancom Router)

Lancom Router:

Port forwarding to 192.168.8.239 (except for the ports of the telephone system).

At the USG 110 nothing was changed except for the WAN port. Why could it be that the guest WLAN does not work?

greetings