Thanks folks. I will speak to Raymarine. I tend to doubt the firmware compatibility cause as the maps and head-unit, while older, are the same vintage and have been getting along nicely until very recently. I can sometimes influence the symptoms by removing, cleaning and reinstalling the map-chips. This is working with less and less success. I suspect it may be dirty contacts on the buss connectors inside the RL.
One last call out on that specific question, anyone know if or how these internal pick-ups should be cleaned?