CompactLogxi L35E v17.4 PLC Locking UP

We have a system containing only (2)CompactLogix L35E with (2) GE Fanuc HMIs and (9)Opto EB2 I/O racks. These devices are connected over a Fiber-Ethernet network with multiple RS900 Switches. About once a week one or both PLCs are locking up.

By locking up I mean no longer controlling the equipment or reporting values to the HMI screens. We are getting the following information on the front of the processor:

Run LED - Solid Green
I/O LED - Flashing Green - but all I/O racks appear to be responding to ping and can monitor using Opto PAC Manager.
OK LED - Solid Green
DCHO LED - Solid Green
MS LED - Solid Green
NS LED - Flashing Green
Link LED - NOT LIT

I have tried to go online with the locked up controller through RSLogix 5000. Cannot connect. Cannot see the device through RSWho (red X). Cannot even ping the PLC through the cmd window of PC.

The only way we are able to get processor back online is to power cycle the locked PLC.

The only other indicator that something is wrong in the system is the NS LED on the front of the Opto EB2 is Solid Red. (This turns green once the PLC is power cycled and connection is re-established).

Please help!

The Link LED's not lying: this controller isn't connected to an Ethernet port anymore. That's consistent with it not responding to RSWho, HTTP, or PING.

See if you can go online with the CompactLogix using the serial port. That will confirm that the controller is OK and the problem is in the Ethernet side.

Does the RS900 switch provide any diagnostics that indicate what's going on with that port ?

I always recommend Auto-Negotiation when both sides support it; are both the switch port and the CompactLogix port configured for Ethernet Auto-Negotiation ?

I will try and go online through the serial port next time it goes down. I didn't have my serial cable with me last time.

The RS900 has no diagnostic information for any of the occurences, on the dates of failures, I only see standard RS900 diagnostic info.

I have all copper ports on the RS900s set to Auto-Negotiate, the Fiber ports do not have Auto-Neg available (only 100M).

Both of the Processor Ethernet cards are set to Auto-Negotiate.

Thanks.