Random NIC lockups using CS8900-CQ3

We are using Cirrus CS8900-CQ3 NICs (3.3V) on an embedded application (QNX V6.3-SP2 on x86) and about once every couple of weeks a unit will lose network comms, you can’t ping/telnet in or out.
From the unit (via a serial console), a ping to “localhostâ€