Hello, I am looking for some help to find a solution to my problem :
I created 2 ABP devices, on V3, 78 days ago. I was using them through a webhook without any trouble until last saturday (2 days ago) for one of them. The other is still functioning properly.
On the console, I still can see both messages from both devices flowing through my TTIG V3 gateway regularly , their FCnt are increasing regularly also ( period is about 5 minutes).
I have created one application for each device ; both are identical functionally speaking and have been functioning properly for 78 days.
Since 2 days, one application is dumb and I don’t see how to find where is my problem as far as I have not done any modification neither on device nor on application or gateway as far as everything was fine.
I would really appreciate if someone could give me some hints.
Thanks for your help.
Paul
SOLVED 
According to à friend indication, on the device setting I have changed the frame coûter width from 16 to 32.
Immediately, operation has recovered.
I can’t explain why it works but it works fine since this small change
Let me confirm that the box Reset frame coûter Is checked since thé beginning.
Frame counters are supposed to be 32 bits, and while only 16 bits are transmitted in the packet, the entire value is used in calculating the Message Integrity Check (MIC).
Thus if either end disagrees about standard 32-bit vs variant 16-bit frame counter mode, then once the upper 16 bits are non-zero, they end using all 32 bits on the MIC calculation will get a different answer than the end using only 16 bits, and all traffic in that direction will be rejected as invalid.
That wouldn’t really help since it doesn’t make the node reset its frame counter, it only allows the network to accept technically illegal packets where the node has done such a reset, eg, when being power cycled or getting a new firmware.
Technically LoRaWAN requires a node to retain its frame count value even across such events.
To Cslorabox :
Thanks for the clarification. I think I have understood .
I will transfer your explanation to my friend.
Regards
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