Missing data packages when constantly transmitting with W5500

Hello I have used iolibrary and example from here

link

to setup my ATSAMD21 curiosity nano and ETH WIZ clck. SAMD21/W5500 configures and connects to my pc. I can send and receive data.

When I was trying to see what can I achieve max with data rates I saw that while constantly transmitting I can not receive data sent from hercules sometimes.

I constantly transmit loop count in main as data. Which starts from 1 and increment whenever it loops.
I randomly send 1 byte of data which is character ‘0’ and It should toggle on board led. Onboard LED does not toggle sometimes…

I was using hercules I tried different software sockettest 3.0.0 and it seems to be problem with hercules not the embedded software.

Are you using the ioLibrary we provide?
The link is performance when ioLibrary and SPI communication use.
https://docs.wiznet.io/Product/iEthernet/W5500/Application/spi-performance