Multitech Gateway Bridge onboard - Downlink not sent

Hi,

I am new to both LoRaWAN and chirpstack. I have configured a multitech conduit AEP by converting it to an mLinux version and installed the lora packet forwarder usb (1.4.1 r11) and gateway bridge 3.4.0_r1 (I tried 3.7.1_r1 with the same results) following the guide on chirpstack.io. I setup the network and application server on Azure again following the guide on chirpstack.io.

Messages sent from a lora device can be seen on the application server and the device successfully joins. On a SDR I can clearly see the uplink and the downlink messages. But when the next message is sent to the server, I expect a downlink to change the spreading factor on the device. When I do a tcpdump on the gateway (sudo tcpdump -AUq -i lo port 1700) I can see the uplink data as well as the expected downlink data, but the downlink is never sent. I can see this on a SDR. The periodic status message also shows that the downlink was sent. Here is an extract of the tcpdump with a rx packet that was successfully received as wel as a tx packet that is not sent out:

19:43:29.106349 IP localhost.49233 > localhost.1700: UDP, length 216
E...A.@.@............Q........[.........{"rxpk":[{"tmst":4057247420,"chan":6,"rfch":0,"freq":867.700000,"stat":1,"modu":"LORA","datr":"SF12BW125","codr":"4/5","lsnr":10.5,"rssi":-56,"size":29,"data":"QGBGBgCACwAChDHQ4sCACt/dPUczm+P10l0ynwY="}]}                                                                                                                                                                                                                                                                                                                                                                                                                                         
19:43:29.139901 IP localhost.1700 > localhost.49233: UDP, length 4
E.. B.@.@..............Q......[.
19:43:30.939511 IP localhost.1700 > localhost.35005: UDP, length 195
E...B.@.@.......................{"txpk":{"imme":false,"rfch":0,"powe":14,"ant":0,"brd":0,"tmst":4058247420,"freq":867.7,"modu":"LORA","datr":"SF12BW125","codr":"4/5","ipol":true,"size":17,"data":"YGBGBgCFCgADUv8AAb88VvY="}}                                                                                                                                                                                                                                                                                                                          
19:43:39.172012 IP localhost.35005 > localhost.1700: UDP, length 12
E..(C.@.@..................'..k.........
19:43:39.178644 IP localhost.1700 > localhost.35005: UDP, length 4
E.. C.@.@.....................k.
19:43:49.304192 IP localhost.35005 > localhost.1700: UDP, length 12
E..(DL@.@..v...............'.g..........
19:43:49.311821 IP localhost.1700 > localhost.35005: UDP, length 4
E.. DM@.@..}.................g..
19:43:56.354142 IP localhost.49233 > localhost.1700: UDP, length 158
E...G.@.@............Q..................{"stat":{"time":"2020-03-24 17:43:56 GMT","lati":-25.00000,"long":28.00000,"alti":1600,"rxnb":2,"rxok":2,"rxfw":2,"ackr":100.0,"dwnb":2,"txnb":2}}                                                                                                                                                                                                                                                                                                                          
19:43:56.377596 IP localhost.1700 > localhost.49233: UDP, length 4
E.. G.@.@..............Q........

I have no idea of where else to look and what to try. Any help will be appreciated.