My X3 seems to have a problem. Every 24-48 hours one of the two units stops mining. Always the same unit.
The PSU and NIC LEDs look normal, the fans are running, and the blue "heartbeat" LED visible through the left front fan is blinking as normal.
So far as abnormal LEDs, there are yellow LEDs visible through the rear fans (I assume these LEDs indicate that the hashing modules are idle), and the blue activity LEDs on the front do not blink as the normally do when mining.
The unit is unresponsive on the network. It does not respond to ARP requests, and of course is equally unresponsive to ICMP pings and HTTP(S) requests (since those require ARP to work).
Yesterday I swapped the PSUs between the two units. The problem did not follow the PSU. The same miner still has the same problem.
(Both units are running software V1.8.)