I believe that your control moved away from the orange fiber optic cables in favor of the fieldnet I/O cabling. The optics were known for getting broken or cracked easily when someone would carelessly dig in the electrical box. The newer Fieldnet used a firewire communication system like high speed ethernet to talk between components. Yours is apparently having trouble communicating with the panel, so I would check the communication cables first and then the panel second as it may be having a problem electronically. If you have similar machines, it may be possible to swap components to see if the problem moves with the swapped item.
Sometimes it is as simple as unplugging and replugging the cable to get rid of some slight corrosion that builds up in the connector over time. Sometimes it is an indicator of boards going bad or having solder connections decay and crack over time.
Best regards,