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We think this was the cause of the problem to receive duplicate data from the device because according to the Wire Shark logs device didn't properly receive the confirmation from the server. We noticed before the device sends duplicate data at that time period, there were few entries of server keep trying TCP Retransmission/ TCP DUP ACK (see the attached - black highlighted rows). We took a tcpdump from the server and examined with the Wire Shark software. Basically if the device didn't receive any information from the server it keep retransmitting the duplicate data.

This only happens if the IOT device lost or got interrupted the connection with the server.

Often times we noticed the server receive duplicate data. Both end send it's data receive confirmation to each other, in order maintain it's communication and accept the next respective message. We have an application which it receive data from a TCP protocol (IOT device) to our Ubuntu server.