@bena: the network register values (ESTAT.BUFFER and EIR.RXERIF) are only for ENC28J60. These don’t exist for W5500, which uses hardware TCP/IP stack. I don’t know what’s the root cause of the issue with W5500 since so far I haven’t heard of hanging issue with W5500 from the other users.
One thing you can try is when the hanging happens, open a browser and type in:
http://x.x.x.x/ja
or
http://x.x.x.x/su
where x.x.x.x is your OpenSprinklers IP. If you use a port that’s not 80, you also need to explicitly specify the port number, such as x.x.x.x:port_number
See if you get a response. If so, that means the Ethernet controller is still working, the issue is somewhere else.