W5100 send RST after receive ACK in 3-way handshake

Hi All
I got problem with IP chipset W5100 in server mode.
Chipset is trying to connect to server, send SYN to server. Receive ACK and then send RST :frowning_face:

Chipset IP, Server IP

Connection is establish due to TCP retranssmition but RST shouldn’t be send.
Please advice.

Hi All
I fixed problem.
Source port was the same for all outgoing connection.
I changed it to random and problem disappeared.