We're seeing an issue here as well with Ethernet.begin on some Industruino 1286 boards with Wiznet W5500 ethernet modules.
We've got three units. One unit works perfectly, one hangs at Ethernet.begin consistently and one worked a couple of times but otherwise hangs at Ethernet.begin. We've tried powercycling the Ethernet modules but that doesn't help.
So we suspect either an intermittent software timing/config issue on startup or the hardware issue with the Ethernet module circuitry being close to design tolerance in some way -- so some units are just inside tolerance and others just outside tolerance.
Could a schematic for the Ethernet module be shared?
I have used the example of EthernetIndustruino, the emon example is very complete, and works out of the box with an account in emoncms.com
On the other way, almost every program designed to work with the Ethernet library works.
This example for implementing a web server, works:
Have a nice day!
Please try to give a substantial answer. If you wanted to comment on the question or answer, just use the commenting tool. Please remember that you can always revise your answers - no need to answer the same question twice. Also, please don't forget to vote - it really helps to select the best questions and answers!