Device runs out of TCP connections when Achilles TCP monitor is active

During Achilles tests, it turned out that the device runs out of TCP connections.

The Achilles TCP Monitor basically just opens and closes 1 single tcp connection and after some time (~600ms) opens an ew one and closes it again.

This is how it should look like in wireshark:

Sometimes the last FIN from the netX is missing and therefore the TCP connection does not close entirely. This connection then stays open and the next TCP connection gets opened by the Achilles monitor.

If this happens too many times in a row, the device runs out of TCP connection and the Achilles monitor complains.

Find a wireshark capture that shows this situation attached: DETRS590.pcap

It must be analyzed why the device does not send the missing FIN frame.