We have two separate chassis with A-B 1756-L73 Rev. 20.0.1 processors and four EN2T/C ethernet modules. Occasionally, at the worst time, the processor will freeze and when trying to connect, the Run and Program options are grayed out. The only solution we've found is to power off the PLC, unplug all the comm cables, re-apply power and plug cables in one at a time. Unfortunately, this happens during a production run and we don't have a lot of time for troubleshooting and so far have not figured out how to duplicate this anomaly. Hoping someone has seen this and can offer suggestions. Thanks