I bought a Wiz850io module, which is basically the same as the Ethernet2 shield with W5500 on it. I am using Adafruits Ethernet2 library with it and it works perfectly most of the time. However in yet unknown conditions the module enters a state from which I can only bring back with a hardware reset. During this state the indicator leds on the RJ45 connector blink in this pattern: Green blink, short delay, Yellow blink, around 1 second delay, repeat.
A few side notes: I am using an Atmega1284 with most of the Arduino Core and libraries modified to work with this MCU. I am coding in Atmel Studio 7 and use JTAG to upload and debug.
Since I can stop the code I observed that after the module is "stuck", my code stucks as well since it waits for data on SPI, which is done with a while statement.
I didn't find anything in the W5500 nor the Wiz850io documents regarding this state.