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The ICMP destination port unreachable message means the UDP port from which the request was sent has already been closed. So the response hits a closed door. I have seen this in different situations, but the most common one being the DNS request was sent to multiple servers and after one responded, the client stops listening on the port of the request that was not answered yet (ie was slower).
Looking at the traffic surrounding these 3 packets should give some more insight in why this might be happening in your case.
