Unfortunately not an answer to your question, but I have faced the same/similar issue with my devices as well. In theory: This error is supposed to trigger at the event of a replayed uplink packet. However, I have seen it trigger so often and from different devices that I doubt it is actually a replay attack.
I spent a lot of time trying to figure out the source of the problem and at this point I am almost giving up.
In my case, I get a few of these retransmission errors per device after a successful uplink, this happens for a few uplinks and then they stop showing for a while. The timings between the retransmissions are consistent, as well as the timings for the periods of uplinks that are followed up by these errors.
I have different types of devices and the error happens will all of them, which makes me believe that the issue is not at the device side. I also experimented with two different gateways (IMST Lite and Wirnet iFemtoCell) and saw the error in both cases.
@takka-bryan Question: do you have many devices in close proximity from each other? and/or in close proximity to the gateway? I have somewhere around 100 devices and two gateways in one building (two floors).
I am starting to think it could be some sort of echoing/bouncing of the signal between devices’ antennas that generates these replayed uplinks because of their close proximity, but I am not at all an expert in communication or electromagnetism to be sure of that
@brocaar Question: have you seen such behavior when deploying many devices in close proximity from each other?