Meaning of SR register 10H

When I read the SR register, it returns a value of 10H.
This is a value not listed in the data sheet, what does it mean?

environment CPU is RX65N
I/F with W5500 is SPI communication

This value is sending the SYN Packet
This status is abnormal and if the status is maintained, you have to send the close command.

I understand.
Thank you