Nordic Border Router suddenly stopped working


I am currently using Nordic border router image as suggested by Google open thread group as i am using NRF5 SDK examples (sleepy mqttsn-publish example to be precise). The issue which i am facing after using the border router for 1 month continuously, suddenly my otbr has stopped acknowledging the packet send by the end device. 

I can see that the MQTT-SN gateway is acknowledging in Rpi system logs but that acknowledge is unable to reach my end device. Here is the system log for the same. please help  me .... 

Image of the issue  : 

- as you can see there is some conflict between wpan0 and wlan0 

Can anyone please help me ?