Fortiswitch FS-108F DHCP IP Problem over Fiber

We connect a Lancom Router via Fiber to the SFP Port in the FortiSwitch.
We recieve a IP Adress from the LancomRouter on the SFP (tested with TestDevice)

But there is no forwarding of the IP adress to the LAN Ports. So when we connect a device to these Ports they do not get an DCHP IP adress from the Lancom Router.

But when wie try it with a connection via RJ45 from the Lancom Router to a LanPort RJ45 in the Fortiswitch it is all fine and we get a IP on the other Lan Ports of the Switch.

But again we also recive a IP direct on the SFP from the Lancom ROuter if we do this SFP in another Testdevice.

The SFP is FN-TRAN-SX from Forti