Im sooo glad of having found this thread...
This is my story. We're preparing a prototype for a client. When it's finished (almost now) he needs 9 of them
It involves an Arduino Mega, Ethernet Shield, Relay module, RTC, etc...
It all worked flawlessly in my home during development for weeks.
I took it to my office to test it integrated with the server, and after working fine for a minute, we had to reset it...and never ever during the day it worked again.
Ok, the Eth module was a cheap clone, had the bottom side pins (that fit into the arduino) hand-soldered, etc, so it didn't really look that pretty... I assumed it was dead... although all the lights were blinking
So I came back home yesterday, happen to plug it all in my house network...and it works. Absolutely at a losssss here
So after some random google searches, I come to this thread...Check my board and it has a 511 resistor array. I guess different switches have different behaviours with such a wrong terminator resistor.
I will try to get a couple of 100Ohm resistors and see if it works again in my office.
Thanks to everyone involved in finding out this issue here!
I was ready to start buying original boards...Maybe not now.
Will get back here wirth results when I solder the new resistors
Thanks again