Binding-knx: No messages between KNX switch actuator and OpenHAB 2.5.12

Dear OpenHAB community,

In my setup of OpenHAB 2.5.12 with the KNX Binding 2, I fail to communicate with switch actuators. While I have no issues to read out measurement values from a whole range of different sensors and to display them in a sitemap, I can neither operate a switch actuator nor read the status value of the switch actuator.


Bridge knx:ip:WHG_IP "WHG IP Router" [
    Thing device WHG_SA02 "WHG SA02" [
        Type switch :  ch1 "Kanal A" [ ga="1.001:2/4/0+<2/4/3" ]


Switch WHG_DG_Licht "WHG DG Licht" <light> { channel="knx:device:WHG_IP:WHG_SA2:ch1" }

The log files show absolutely no entries when changing the status of the switch actuator on the KNX end. If I slide the switch on the OpenHAB sitemap, I can see in the logfiles that the command is somehow executed, but it appears that no message is sent to the KNX bus, neither is a message received:

tail -f /var/log/openhab2/openhab.log /var/log/openhab2/events.log

2021-03-07 20:14:34.143 [hingStatusInfoChangedEvent] - 'knx:device:WHG_IP:WHG_SA02' changed from OFFLINE (BRIDGE_OFFLINE) to UNKNOWN
2021-03-07 20:14:59.391 [hingStatusInfoChangedEvent] - 'knx:device:WHG_IP:WHG_SA02' changed from UNKNOWN to OFFLINE
2021-03-07 20:17:46.981 [ome.event.ItemCommandEvent] - Item 'WHG_DG_Licht' received command ON
2021-03-07 20:17:46.985 [nt.ItemStatePredictedEvent] - WHG_DG_Licht predicted to become NULL
2021-03-07 20:17:52.077 [ome.event.ItemCommandEvent] - Item 'WHG_DG_Licht' received command OFF
2021-03-07 20:17:52.085 [nt.ItemStatePredictedEvent] - WHG_DG_Licht predicted to become NULL

I am not familiar with the states of KNX devices. At least, I wonder why the switch actuator device is not reported as ONLINE. However, the other devices also remain as OFFLINE, and their measurement values are received by OpenHAB. Please see below how a temperature sensor puts its measurement values onto the KNX bus, and these messages (and similar ones from various other sensors) can be received by OpenHAB:

2021-03-07 20:14:34.347 [vent.ItemStateChangedEvent] - WHG_DG_Dachraum_Abs_Luftfeuchtigkeit changed from NULL to 6.0
2021-03-07 20:14:34.466 [vent.ItemStateChangedEvent] - WHG_DG_Dachraum_Taupunkttemperatur_Messwert changed from NULL to 3.2
2021-03-07 20:14:34.566 [vent.ItemStateChangedEvent] - WHG_DG_Dachraum_Rel_Luftfeuchtigkeit changed from NULL to 32
2021-03-07 20:14:34.670 [vent.ItemStateChangedEvent] - WHG_DG_Dachraum_Temperatur changed from NULL to 21.7
2021-03-07 20:14:34.149 [hingStatusInfoChangedEvent] - 'knx:device:WHG_IP:WHG_RTF07' changed from OFFLINE (BRIDGE_OFFLINE) to UNKNOWN
2021-03-07 20:14:47.277 [hingStatusInfoChangedEvent] - 'knx:device:WHG_IP:WHG_RTF07' changed from UNKNOWN to OFFLINE

Prior to the present network setup, I had both OpenHAB and the KNX IP Router in the same subnet, both having an address in the subnet. In this setup, I had no issues with the switch actuators.

While I actually did not change the hardware setup since then, I configured my router/switch to create a separate VLAN in subnet for KNX and other IoT stuff. At present, the firewall rules between the and the subnets are wide open. My ETS for programming KNX also resides in the subnet, while it needs to connect to the KNX IP Router in the subnet. This works without any problems. I can operate the bus monitor and have read/write access to the KNX bus.

Does anybody have a hint why I can neither read nor write messages between KNX bus and OpenHAB as long as switch actuators are involved?

Best regards,