TCP conversation between nodes seem to be fine, I suspect that first ACK #2049 has been lost, the W5500 unexpectedly receives ACK for #2051, and resends all 4 bytes remaining in the buffer from previous ACK (7e472142). Then IMHO server properly responds.
Do you take this Wireshark log at the server side? Then you may not see whole picture. I advise you to put Windows 7 machine configured as network bridge with Wireshark connected directly to W5500, and then you will be able to see what is going on at the chip’s side. I think you may be surprised that some proxy or router confuses packets or decides for the involved communicating nodes that they need to break up, and instructs W5500 to close its connection from its side and then of course W5500 responds RST on any further packets from the server as its socket is closed.
