Coapclient can not receive data from Coapserver

[SaberPhung]

Hi, I met the issue with the coapserver's response. Server runs on a device and listens to port 5683 and responds to port 5684. I see that stuff from Wireshark.
I used coapclient.py https://github.com/Tanganelli/CoAPthon3/blob/master/coapclient.py
It seems that the response message never reach the client and the client show "giving up" message after the request 4 times.

I'm trying to understand the issue, but not very successfully yet. Looking for some help
coap.zip
Wireshark IEEE802.15.4 decryption key: 7B:E4:39:B7:7D:16:3E:C7:7:73:A:34:A7:A6:34:73